Strategies for Managing Weeds in a Wheat, Red Clover, Vegetable Crop Rotation Transitioning to Organic Production

STRATEGIES FOR MANAGING WEEDS IN A WHEAT, RED CLOVER, VEGETABLE CROP ROTATION TRANSITIONING TO ORGANIC PRODUCTION

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

Karen Janila Amisi, B.Sc. Horticulture M.S. Natural Resources and Environmental Sciences *****

The Ohio State University 2005

Dissertation Committee: Dr. Douglas Doohan, advisor Approved by: Dr. Matthew Kleinhenz Dr. Sally Miller ______Dr. Emmy Regnier Advisor Horticulture and Crop Science Graduate Program

ABSTRACT

Weed management is one of the biggest challenges faced by organic farmers. We investigated the use of two weed control strategies, critical period (CP) of competition and no seed threshold (NST), and the effect of soil amendments for farmers transitioning from conventional to organic production. Field experiments were conducted at the Ohio

Agricultural Research and Development Center in Wooster, OH. In 2001, a 4-year rotation of wheat, clover, cabbage, and processing tomato was established in soil previously in a conventional corn/soybean/forage agronomic rotation. The experimental design was a split plot in a randomized complete block with 4 replications. Main plots were soil amendments (none, raw dairy manure, composted dairy manure). Amendments were applied in spring at the rate equivalent of 101 kg N/ha and incorporated prior to planting. Subplots were weed control strategies; NST, where seedling weeds were removed weekly for the whole season and no weeds permitted to mature seeds in the field, and CP, where plots were kept weed-free for the first 5 weeks of crop growth.

Evaluations included emerged weed communities both in the field and seedbank. Time taken to hand-weed was documented and labor cost of using CP and NST weed management strategies calculated. Yield of tomato and cabbage were recorded. The NST reduced redroot pigweed (Amaranthus retroflexus L.) and commom lambsquarters ii (Chenopodium album L.) by 30 - 62% and 22 - 60% respectively in the rotational crops.

This was corroborated by weed seed data from soil samples taken in the spring following use of CP and NST strategies the previous year. Some significant effects (P ≤ 0.05) were noted among the soil amendment on density of redroot pigweed and common lambsquarters, though no clear trends were observed. Achieving the NST required 33 to

92 % more labor than did the CP. However, the cost of labor required for the NST was not greater than weed control costs typically experienced by organic farmers. In a greenhouse experiment, growth and seed production of redroot pigweed was reduced in field soil amended with livestock manure. Growth and seed production of the weed was greater in soils amended with compost. Rates of manure and compost were equivalent to

2x and 3x those applied to tomato and cabbage in the field experiments.

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Dedicated to Sango, Tumaini, and Rehema

for your patience and understanding.

ACKNOWLEDGMENTS

I would like to thank my advisor, Dr Doug Doohan for his guidance, support encouragement, and patience throughout my studies. I also thank members of my

Student Advisory Committee, Drs M. Kleinhenz, S. Miller and E. Regnier for their help, advice, and use of laboratory facilities to undertake my research work.

I especially want to thank Dr. Annette Wszelaki, for the role she played in organizing the field operations. She was very involved in the field work, provision of data and research information, and was always an encouragement. Thanks also to Bert

Bishop for his help in statistical analysis.

I am grateful to the Department of Horticulture and Crop Science for providing funds that enabled me to complete my studies. This research was supported in part by funding obtained through the Initiative for Future Agriculture and Food Systems

(IFAFS) program of United States department of Agriculture, for which I am very thankful.

I thank the Weed Science laboratory members, Drs John Cardina, Joel Felix, and

Lynn Sosnoskie, Cathy Herms, and Tim Koch, for their advice and help in undertaking various stages of my research work. Each one of them has been a great inspiration.

I am deeply grateful to all the people who helped with various stages of the research work in the field, greenhouse or laboratory. I especially thank Paul McMillen, v

Bob Napier, Sonia Walker, Noah Myers, Josh Reinford, Lee Duncan, Kim Hershberger and Greg Brenneman for all their hard work.

I thank all my friends for their prayers, support and encouragement throughout my studies. I especially thank Mike and Mary Senger, Mary Misner, and Linda Kline. I am very grateful to Barb Kerns, for being ‘mom’ and ‘grandma’ to my family. Thank you for your love and generosity. I will always have a special place for you in my heart.

My deepest gratitude goes to my husband, Sango, son Tumaini, and daughter

Rehema for their immense support. I also thank my family in Kenya for constantly keeping in touch.

Finally I thank God for giving me good health and strength throughout my studies. With Him nothing is impossible.

VITA

July, 25, 1967...... Born, Nairobi, Kenya.

September, 1990 ...... Diploma in Horticulture, Egerton University, Kenya.

November, 1995 ...... B. Sc. Horticulture, Egerton University, Kenya.

May, 2000...... M.S. Natural Resources and Environmental Science, University of Illinois, Urbana-Champaign, IL.

August, 1998 – May, 2000 ...... Graduate Research Assistant, Department of Natural Resources and Environmental Science, University of Illinois, Urbana-Champaign, IL.

September, 2000 – Dec, 2004...... Graduate Research Associate, Department of Horticulture and Crop Science, The Ohio State University, Columbus, OH.

PUBLICATIONS

Amisi, K. J.2000. Alternative Weed Management Systems for Pumpkins. Thesis. University of Illinois, Urbana-Champaign. Amisi, K. J., D. J. Doohan, M. D. Kleinhenz, and S. Miller. 2003. Effect of Critical Period (CP) and No Seed Threshold (NST) weed management strategies in a transitional vegetable organic system. NCWSS Abstr. 58:163. [CD-ROM Computer File]. North Central Weed Sci. Soc. Champaign, IL. Amisi, K. J., D. J. Doohan, M. D. Kleinhenz, S. Miller. 2004. No Seed Threshold and Critical Period weed management in a transitional organic vegetable system. WSSA Abstracts 44:201

FIELD OF STUDY

Major Field: Horticulture and Crop Science.

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TABLE OF CONTENTS

Page Abstract...... ii Dedication...... iv Acknowledgments ...... v Vita ...... vii List of tables ...... x List of figures...... xvi

Chapter 1...... 1 Introduction...... 1 Organic vegetable production...... 2 Crop rotation...... 4 Soil fertility management ...... 5 Weed management in organic vegetable production...... 7 List of References...... 13

Chapter 2...... 19 Weed management strategies for transition to organic: the critical period of competition and the no-seed threshold...... 19 Abstract...... 19 Introduction...... 21 Materials and Methods ...... 27 Results and Discussion ...... 34 Conclusion ...... 41 List of References...... 58

Chapter 3...... 63 Economics of no-seed-threshold weed management and soil amendments in organic tomato and cabbage...... 63 Abstract...... 63 Introduction...... 64 Materials and Methods ...... 68 Results and Discussion ...... 71 Conclusion ...... 74 List of References...... 79

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Chapter 4...... 83 Redroot pigweed (Amaranthus retroflexus L.) growth in compost- and manure-amended soil mixes ...... 83 Abstract...... 83 Introduction...... 84 Materials and Methods ...... 87 Results and Discussion ...... 89 Conclusions...... 93 List of References...... 101

Bibliography ...... 105

Appendices ...... 118 Appendix A: Relative abundance of weeds in field plots and seedbank samples...... 118 Appendix B: Weed control ratings for weed and soil amendment treatments...... 125 Appendix C: Estimated number of redroot pigweed seeds in critical period treatment plots for tomato in 2002 ...... 127 Appendix D: Average monthly weather data at OARDC, Wooster, OH from 2001 to 2004...... 129 Appendix E: Multiple linear regression analyses on the effects of compost- and manure-amended soils on growth parameters of redroot pigweed ...... 131

LIST OF TABLES

Table Page

Table 2.1: Characteristics and applied amounts of compost used on the organic transition plots. Abbreviations: C = carbon, N = nitrogen, P= phosphorus, K = potassium, wt. = weight. Elemental analysis values (%) for total N, P, and K are raw and based on moisture content...... 45

Table 2.2: Characteristics and applied amounts of manure used on the organic transition plots. Abbreviations: C = carbon, N = nitrogen, P= phosphorus, K = potassium, wt. = weight. Elemental analysis values (%) for total N, P, and K are raw and based on moisture content...... 45

Table 2.3: Weeds observed in the field plots and weed seedbank soil samples. Life cycle: SA = summer annuals, WA = winter annual, CP = creeping perennial, SP = simple perennial, and B = biennial. Field plots and Seedbank samples: P = weed present, NP = weed not present...... 46

Table 2.4: The effect of weed management strategies (CP and NST) on average number of redroot pigweed (AMARE) and common lambsquarter (CHEAL) seedlings / plot (56 m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 1. For both AMARE and CHEAL: NP = weed not present at the time of counting; dash ( - ) = no data; Total= total number of weeds counted for 2, 3, and 5 WAT for each rotation sequence. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns...... 48

Table 2.5: The effect of weed management strategies (CP and NST) on average number of redroot pigweed (AMARE) and common lambsquarter (CHEAL) seedlings / plot (56 m2) 2, 3, and 5 weeks x

after transplanting (WAT) for Rotation 2. For both AMARE and CHEAL: NP = weed not present at the time of counting; dash ( - ) = no data; Total= total number of weeds counted for 2, 3, and 5 WAT for each rotation sequence. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns...... 49

Table 2.6: The effect of weed management strategies (CP and NST) on average number of redroot pigweed (AMARE) and common lambsquarter (CHEAL) seedlings / plot (56 m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 3. For both AMARE and CHEAL: NP = weed not present at the time of counting; dash ( - ) = no data; Total= total number of weeds counted for 2, 3, and 5 WAT for each rotation sequence. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns...... 50

Table 2.7: The effect of weed management strategies (CP and NST) on average number of redroot pigweed (AMARE) and common lambsquarter (CHEAL) seedlings / plot (56 m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 4. For both AMARE and CHEAL: NP = weed not present at the time of counting; dash ( - ) = no data; Total= total number of weeds counted for 2, 3, and 5 WAT for each rotation sequence. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns...... 51

Table 2.8: The effect of weed management strategies on average number of emerged redroot pigweed (AMARE) and common lambsquarter (CHEAL) / plot (56 m2) from soil seedbank samples for Rotations 1, 2, 3 and 4. Means followed by different letters within each row are significantly different at P ≤ 0.05 within weed species...... 52

Table 2.9: The effect of soil amendment (control, compost, and manure) on average number of redroot pigweed (AMARE) and common lambsquarters (CHEAL) seedlings / plot (56m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 1. For AMARE and CHEAL: NP = weed not present at the time of counting; dash (-) = no data; Total = total number of weeds counted for 2, 3 and 5 WAT for each rotation sequence. No soil amendment was applied in the Clover and Wheat. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns ...... 53

Table 2.10: The effect of soil amendment (control, compost, and manure) on average number of redroot pigweed (AMARE) and common lambsquarters (CHEAL) seedlings / plot (56m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 2. For AMARE and CHEAL: NP = weed not present at the time of counting; dash (-) = no data; Total = total number of weeds counted for 2, 3 and 5 WAT for each rotation sequence. No soil amendment was applied in the Clover and Wheat. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns ...... 54

Table 2.11: The effect of soil amendment (control, compost, and manure) on average number of redroot pigweed (AMARE) and common lambsquarters (CHEAL) seedlings / plot (56m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 3. For AMARE and CHEAL: NP = weed not present at the time of counting; dash (-) = no data; Total = total number of weeds counted for 2, 3 and 5 WAT for each rotation sequence. No soil amendment was applied in the Clover and Wheat. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns ...... 55

Table 2.12: The effect of soil amendment (control, compost, and manure) on average number of redroot pigweed (AMARE) and common lambsquarters (CHEAL) seedlings / plot (56m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 4. For AMARE and CHEAL: NP = weed not present at the time of counting; dash (-) = no data; Total = total number of weeds counted for 2, 3 and 5 WAT for each rotation sequence. No soil amendment was applied in the Clover and Wheat. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns ...... 56

Table 2.13: The The effect of soil amendment (control, compost, and manure) on average number of emerged redroot pigweed (AMARE) and common lambsquarters (CHEAL) seedlings / plot (56m2) from soil seed bank samples for Rotations 1, 2, 3, and 4. For AMARE and CHEAL: dash (-) = no data for clover. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species column ...... 57

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in 2004); CP = critical period for 5 weeks after planting and NST = no seed threshold for entire season...... 75

Table 3.2: Effect of soil amendments (no amendment (control), raw manure or composted manure) and weed treatments on yield of organic processing tomatoes in 2001...... 76

Table 3.3: Effect of soil amendments (no amendment (control), raw manure, or composted manure) and weed treatments on yield of organic processing tomatoes in 2002. Means followed by different letters under amendment columns within each row are significantly different at P ≤ 0.05 ...... 76

Table 3.4: Effect of soil amendments (no amendment (control), raw manure, or composted manure) and weed treatments on yield of organic processing tomatoes in 2003...... 77

Table 3.5: Effect of soil amendments (no amendment (control), raw manure, or composted manure) and weed treatments on yield of organic cabbage in 2001. Means followed by different letters under amendment columns within each row are significantly different at P ≤ 0.07...... 77

Table 3.6: Effect of soil amendments (no amendment (control), raw manure, or composted manure) and weed treatments on yield of organic cabbage in 2002. Means followed by different letters under amendment columns within each row are significantly different at P ≤ 0.05...... 78

Table 3.7: Effect of soil amendments (no amendment (control), raw manure, or composted manure) and weed treatments on yield of organic cabbage in 2003. Means followed by different letters under amendment columns within each row are significantly different at P ≤ 0.05 (*) and P ≤ 0.01 (**)...... 78

Table 4.1: Media mixes used in redroot pigweed growth studies...... 95

Table 4.2: Effect of compost- and manure-amended soils on internode length (cm) of redroot pigweed (14 DAP) in Trial 1 and 2. Means followed by different letters within a column are different at P ≤ 0.05 ...... 95

Table 4.3: Effect of compost- and manure-amended soils on plant height (cm) of redroot pigweed in Trial 1. Means followed by different letters within a column are different at P ≤ 0.05...... 96 xiii

Table 4.4: Effect of compost- and manure-amended soils on plant height (cm) of redroot pigweed in Trial 2. Means followed by different letters within a column are different at P ≤ 0.05...... 97

Table 4.5: Effect of compost- and manure-amended soils on number of leaves and leaf area (cm2) of redroot pigweed (18, 23, and 30 DAP) in Trial 1. Means followed by different letters within a column are different at P ≤ 0.05 ...... 98 Table 4.6: Effect of compost- and manure-amended soils on number of leaves and leaf area (cm2) of redroot pigweed (18, 23, and 30 DAP) in Trial 2. Means followed by different letters within a column are different at P ≤ 0.05 ...... 99

Table 4.7: Effect of compost- and manure-amended soils on fresh weight (g), dry weight (g) and number of seeds of redroot pigweed (63 DAP) in Trial 1 and 2. Means followed by different letters within a column are different at P ≤ 0.05 ...... 100

Table A.1: Relative abundance of weeds present in the tomato and cabbage plots in 2001 ...... 120

Table A.2: Relative abundance of weeds present in the weed seedbank soil samples from the tomato plots. Abbreviations: F = fall, SP = spring ...... 121

Table A.3: Relative abundance of weeds present in the weed seedbank soil samples from the cabbage plots. Abbreviations: F = fall, SP = spring ...... 122

Table A.4: Relative abundance of weeds present in the weed seedbank soil samples from the wheat plots. Abbreviations: F = fall, SP = spring ...... 123

Table A.5: Relative abundance of weeds present in the weed seedbank soil samples from the clover plots. Abbreviations: F = fall, SP = spring ...... 124

Table B.1: Weed control ratings (%) showing the effect of weed treatments (NST and CP) on weed composition in tomato and cabbage plots immediately after harvest in 2001. Weed control was rated visually and expressed as a percentage, where 0% = poor and 100% = excellent...... 126

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Table B.2: Weed control ratings (%) showing the effect of amendments (control, compost, and manure) on weed composition in tomato and cabbage plots immediately after harvest in 2001. Weed control was rated visually and expressed as a percentage, where 0% = poor and 100% excellent...... 126

Table C.1: The average number of redroot pigweed seeds estimated per plot (56 m2) in the critical period (CP) treatment plots for tomato in 2002 ...... 128

Table D.1: Average monthly weather data for OARDC, Wooster Ohio. Abbreviations: ppt = precipitation, Temp = temperature, C = centigrade...... 130

Table E.1: Multiple linear regression equations for the effect of compost- and manure-amended soils on plant internode length (cm) and height (cm) of redroot pigweed in Trial 1 at P ≤ 0.05. Abbreviation: DAP = Day after planting...... 132

Table E.2: Multiple linear regression equations for the effect of compost- and manure-amended soils on plant internode length (cm) and height (cm) of redroot pigweed in Trial 2 at P ≤ 0.05. Abbreviation: DAP = Day after planting...... 133

Table E.3: Multiple linear regression equations for the effect of compost- and manure-amended soils on number of leaves and leaf area of redroot pigweed in Trial 1 at P ≤ 0.05. Abbreviation: DAP = Day after planting ...... 134

Table E.4: Multiple linear regression equations for the effect of compost- and manure-amended soils on number of leaves and leaf area of redroot pigweed in Trial 2 at P ≤ 0.05. Abbreviation: DAP = Day after planting ...... 135

Table E.5: Multiple linear regression equations for the effect of compost- and manure-amended soils on plant fresh weight (g), dry weight (g) and number of seeds of redroot pigweed at 63 days after planting (DAP) in Trial 1 at P ≤ 0.05 ...... 136

Table E.6: Multiple linear regression equations for the effect of compost- and manure-amended soils on plant fresh weight (g), dry weight (g) and number of seeds of redroot pigweed at 63 days after planting (DAP) in Trial 2 at P ≤ 0.05 ...... 137

LIST OF FIGURES

Figure Page

Figure 2.1: Plot map showing location of soil amendments in 2001 ...... 43

Figure 2.2: Plot map showing location of weed treatments in 2001...... 44

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CHAPTER 1

INTRODUCTION

Sustainable agriculture has been defined as a “philosophy and system of farming based on a set of values that involve benign management procedures to conserve all resources, minimize waste and environmental impact, prevent problems, and promote agroecosystem resilience, self-regulation, evolution, and sustained production for the nourishment and fulfillment of all” (MacRae et al., 1989). It aims to incorporate the long-term maintenance of natural resources and agricultural productivity with minimal adverse environmental impacts, adequate economic returns to farmers, and the fulfillment of social needs of farm families and communities (Wyse, 1994).

Concerns over environmental contamination by fertilizers and pesticides, coupled with questions over social, economic, and health-related impacts of conventional agricultural systems, have led to efforts to improve agricultural sustainability through research, education and policy initiatives (NRC, 1991; Liebman, 1992). As a result, there is a growing interest in the design and management of agroecosystems that rely primarily on manipulation of ecological interactions rather than application of agrochemicals to maintain soil productivity and manage pest populations (Stinner and

House, 1989). Organic farming is one of several approaches to sustainable agriculture. It 1

refers to production systems, which avoid or largely exclude synthetic fertilizers, pesticides, or growth regulators. Organic systems tend to rely on crop rotation, in situ mulches or organic amendments, mechanical cultivation, mineral-bearing rocks, and techniques of biological pest control to maintain soil productivity and tilth, supply plant nutrients, and control, weeds, insects, and diseases (Grubinger, 1999; U.S. Dept.

Agriculture, 1980).

Organic farmers have identified weed management as one of their primary concerns. Increasing crop diversity through rotation can reduce weed density and prevent major shifts in weed community composition toward particularly noxious species. Management of compost and manure is important to both soil quality and weed dynamics. The main objective of this study was to investigate the effects of nutrient- and weed-management techniques on weed emergence, soil weed seedbanks and weed population dynamics in vegetable production during the transition from conventional to organic management.

Organic vegetable production

Vegetable production is a dynamic and major segment of the United States economy. Although a small industry, organic vegetable production is gaining importance in the United States agriculture sector. With increasing demand for fresh farm produce, vegetables may play a major role in improving farm income. Organic products typically sell for a much higher price than their conventional counterparts. The profitability of organic vegetable farming varies, however, and few studies have assessed its long-term prospects. 2

Organic vegetable production may be an economically viable alternative for producers. Producers are usually registered and/or certified. Registration is a legal mechanism that permits a grower to sell produce or a product as organic. Certification is a process whereby an organic production, handling, processing, or retailing enterprise is certified as following organic production and handling practices. Presently, registration is a legal requirement, and certification is a private process independent of government oversight, used by growers and marketers to maintain the integrity of the organic product. Certification is a much more complete and comprehensive process than registration, requiring an annual farm inspection, maintenance of crop management, handling, and input records (for auditing), and an affidavit of compliance. The certifying agency may also require a comprehensive long-term program for soil and pest management (Gaskell et al., 2000b).

Once registration and certification are complete, use of the terms ‘organic’ and

‘certified organic’ are permitted only after a passage of at least 3 years during which no prohibited product was used. However, if the grower follows organic production practices but has not yet completed the minimum time required for registration as organic, the produce may be marketed as ‘transitional organic’.

The transition period from conventional to organic farming lasts a minimum of 3 years. During this period, crop yields are usually unstable, premium prices unavailable, and weed and pest (disease and insect) pressure severe since the use of herbicides and pesticides are withdrawn (COG Field Crop Handbook, 1992). Organic farming systems depend strongly on the integration of major management factors. Farmers must carefully

consider crop rotation, soil fertility, and soil management when planning a transition to organic farming.

Crop rotation

Crop rotation involves growing different crops in recurring sequence on the same unit of land. Rotation sequences may extend over several years or be compressed into a single year. Rotations may also include the use of non-harvested crops grown for soil improvement (green manures), soil conservation (cover crops), and nutrient retention

(catch crops) when the main cash or feed crops are not in the field (Liebman and Ohno,

1998).

Potential benefits of crop rotation depend on the specific crops used and rotation length, and include: 1) improvement in soil physical characteristics such as decreased bulk density, improved aggregate stability, and water retention (MacRae and Mehuys,

1985; Bullock, 1992, Karlen et al., 1994); 2) reduced soil erosion (Helper et al., 1984,

1985; Gatzer et al., 1991); 3) increased availability of nitrogen (N) to subsequent crops following N2 fixation by legumes (Heichel and Barnes, 1984; Voss and Shrader, 1984;

Fox and Pielielek, 1988; Frye et al., 1988; Hesterman, 1988); 4) reduced nitrate leaching

(Shipley et al., 1992; Jackson et al., 1993) ; 5) reduced incidence and severity of certain soil-borne crop diseases (Sturtz and Beiner, 1987; Dabney et al., 1988; McEwn et al.,

1989); 6) reduced densities of certain insect pests (Lashomb and Ng, 1984; Wright,

1984; Brust and King, 1994); and 7) reduced weed density, whether or not herbicides are used (Schreiber, 1992; Martin and Felton, 1993; Liebman and Dyck, 1993; Blackshaw,

1994). 4

Soil fertility management

Organic farmers have identified the following soil fertility and /or soil tilth management issues of greatest concern on their farms: building and maintaining organic matter levels, developing soil biological activity, reducing soil compaction, balancing soil pH, and balancing soil nutrients (Walz, 1999). Soil nutrient availability can be improved through a combination of crop rotation, tillage, cultural practices, and soil amendment.

Organic matter constitutes the active or “living” component of the soil, affecting physical and chemical properties (Swiader et al., 1992). Organic matter affects plant growth, promotes development of soil aggregates, improving drainage, soil tilth, and structure. Addition of organic matter to the soil is important to maintain soil structure.

Organic matter can be added to the soil by various methods using green manure crops, cover crops, crop residues, animal manures, mulches, and composts (Precheur et.al.

2004).

However, the use of fresh organic matter in close proximity to planting of vegetables may cause problems that include burning from rapid decomposition, formation of excessively aerated layers and pockets, which interfere with water movement, locking up of available nitrogen by decomposition bacteria, mechanical interference to plowing and cultivation, and formation of toxic organic compounds, under certain anaerobic conditions (Precheur et.al.2004; Swiader et al., 1992).

Soil organic matter (SOM) is linked to desirable soil physical, chemical, and biological properties and is closely associated with soil productivity (Stevenson, 1982;

Tate, 1987). Changes in biologically active SOM are linked to a transition effect. The 5

transition from conventional to organic production normally involves a period of suppressed yield followed by a return to yield similar to conventional production

(Brusko, 1989; Liebhardt et al., 1989). This “transition effect” has been attributed in part to changes in the soil’s biological, chemical, and physical properties governing nutrient cycling, plant growth and development (Wander et al., 1994).

Soil fertility affects weeds, but not much work has been done on the manipulation of soil fertility to manage weed populations. Fertilizer is added to improve crop yield, but often weeds are more competitive with crops at higher nutrient levels. At low weed densities, added fertilizers, particularly nitrogen, will increase crop yield and make the crop a more vigorous competitor. At high weed densities, added nutrients favor weed over crop growth (DiTomaso, 1995). The primary plant nutrients are nitrogen, phosphorus and potassium. Weeds have a large nutrient requirement and will absorb as much or more than crops. Nitrogen is the first nutrient to become limiting between weed and crop competition. The nitrate ion is highly mobile and not held strongly in soil.

Movement of phosphorus and potassium is slow and occurs over shorter distances.

Competition for these nutrients often occurs after plants are mature and have extensive root development (Zimdahl, 1999).

Manure and compost (though important nutrient sources in organic farming) are often sources of weed introduction and dispersal in cropland. Hence, management of manure and compost has great importance to both soil quality and weed dynamics. The density of viable weed seeds in animal manure is a function of the types of plant materials fed to them. Poultry manure contains few viable weed seeds because they are broken down in the gizzard. Dairy manure may contain thousands of viable seeds per ton 6

because the seeds of certain species survive passage through the animal’s digestive system. Manure of milking cows fed on concentrate feeds may have fewer seeds than dry cows, which are fed coarse and weedier forages (Cudney et al., 1992; Sarapatka et al.,1993; Mt. Pleasant and Schlather, 1994). Handling and storage of amendments can also affect weed seeds. Composting kills weed seeds contained in manure and plant materials through seed exposure to high temperatures, organic acids, methane and carbon dioxide produced during the fermentation process (Sarapatka et al.,1993).

Weed management in organic vegetable production

Weed management is one of the biggest challenges organic growers face. Weed control is particularly important during transition, when large and unexpected changes in weed population dynamics may occur as the ecological dynamics of the farming system and the farmer’s knowledge and management skills develop (Kristiansen et al., 2001).

Findings from the 1999 Organic Farming Research Foundation (OFRF) national survey show that 62% of 1,179 respondents ranked weed management as a top research priority.

Weeds were also ranked as the top requirement for organic production information, the greatest barrier to transition, and the second most common focus for farmers’ own on- farm research activities after variety trials (Walz, 1999).

A plant becomes a weed when it is perceived to be interfering with a production cycle, causing crop yield reductions, contamination, or some other problem. Some weeds are highly invasive while others may have little impact on production. The OFRF survey

(1999) listed foxtail, pigweed, and quackgrass as the most frequent problem weeds, and bermudagrass, johnsongrass, and bindweed as the most difficult weeds to manage. The 7

latter three weeds tend to have persistent underground parts like rhizomes, or are heavily seeding annuals. Weeds are only a problem if they reduce crop yields or complicate harvest problems.

No single weed management strategy will apply to all organic farms. Thus, weed management should be taken as a long-term, dynamic process. Standard weed control approaches focus on providing the crop with a competitive advantage rather then elimination of all weed species. Organic weed management relies on mechanical, biological, and cultural methods, but these methods must be used in integrated, multi- faceted approaches. In addition, timeliness, vigilance, persistence, and flexibility are important factors in effective weed management (Kristiansen, 2000). The most frequently used organic weed management practices are manual and mechanical tillage, crop rotations, use of cover and smother crops, slashing and numerous cultural strategies

(COG Field Crop Handbook, 1992; Walz, 1999; Kristiansen et al., 2001).

Crop rotation is regarded as a cornerstone of organic farmers’ methods of achieving weed, insect and disease management (Walz, 1999). However, in studies examining the effects of crop rotation on weed dynamics, crop rotation is often confounded with herbicide rotation, making it difficult to separate ecological from chemical effects. Increasing crop diversity through rotation can reduce weed seed and plant density (Forcella and Linsdtrom, 1988; Blackshaw, 1993; Martin and Felton, 1993) and prevent major shifts in weed community composition toward particularly noxious species. These effects are due to the creation of complex, unstable patterns of resource availability, soil disturbance, and mechanical damage that reduce weed survival, growth and reproduction (Blackshaw, 1993; Martin and Felton, 1993). Weed biology, ecology, 8

and population dynamics factors, such as weed seedling emergence and survival, weed growth and seed production, are also affected by crop rotation.

The greatest source of weed infestation in cropland is the weed seedbank (Cavers and Benoit, 1989). The weed seedbank is composed of seed produced on site and seed moved (dispersed) into the area. Weed seedbanks are dormant or active and changes in the composition of the seedbank include both inputs and losses. Studies show that estimating the viable seedbanks is important in understanding seedbank dynamics

(Cardina and Sparrow, 1996; Ambrosio et al., 1997). Viable seeds in the soil seedbank have been estimated using seedling emergence and direct extraction from the soil.

Although the seedling emergence technique has many benefits (Forcella et al., 1992,

1997; Grundy et al., 1996), its main limitation is that unknown quantities of dormant seed remain in the soil. Viable seed can also be estimated by direct extraction of seeds from the soil and either identifying and counting them (Fay and Olson, 1978; Gross,

1990) or germinating seed under uniform environmental conditions (Decker, 1999).

Economic thresholds have been developed to provide a more rational approach to weed management. The economic threshold concept was originally developed for management of arthropod pests and is based on the understanding of arthropod population biology. Adopting a management strategy for weeds that was developed for maintaining arthropod populations below a damaging level, referred to as the economic injury level (EIL), is not ecologically sound. Factors regulating the populations of the two pests differ. An economic threshold (ET) for arthropod management is defined as the pest population at which treatment should be initiated to stop the population from increasing to EIL. Weed science has adopted ET to be the synonymous with EIL. This 9

leads to maintenance of a relatively high seedbank as weeds at or below the ET density are allowed to produce seed (Norris, 1999). Insects tend to fly into fields annually whereas weeds (as seed) are resident in fields and create problems. Even if an EIL is not achieved in one year, seed rain would ensure that an EIL would be attained in subsequent years.

Problems also exist with the way the ET concept has been applied to weed management. Weed science seems to have equated the ET with EIL. First, this creates a problem in relation to the timing of initiation of control measures. Secondly, the ET concept as applied to weed management aggravates development of herbicide resistant weeds. Thirdly, with respect to invading weed species, the ET concept leads to establishment of the seedbank before any control action is taken (Norris, 1999).

Thresholds help in determining if weed density and interference are sufficient to justify control measures. Norris (1999) has proposed a fairly new concept referred to as

No Seed Threshold (NST). This threshold implies that weeds present or remaining in a field should not be permitted to set seed (Norris, 1995). Some vegetable farmers in

California have successfully adopted NST in their weed management program, demonstrating that it is a strategy that can be used to stop weed reinfestation. This concept has potential application for high value crops like organically grown vegetables.

However, long-term studies need to be done to develop reliable data on the impact of

NST on weed population dynamics.

Norris (1999) argued that utilization of NST would result in reduction of the weed seedbank with each germination event. Since weeds are normally present in patchy distributions, impacts of patchiness on competition, crop losses, and weed population 10

assessment must be considered (Cardina et al., 1997). NST requires only presence/absence information, reducing the need to evaluate weed patchiness. Adoption of NST would eliminate the problem of the development of herbicide resistance, as no seed is produced and thus no genes are passed on (Norris, 1999). The main disadvantage of NST is that it may be labor intensive and costly during the first years. However, subsequent reductions in weed populations in future years may offset earlier adoption costs. The NST strategy implies an integrated approach to weed management requiring the use of hand labor to remove weeds that escape other management tactics. Currently, no data exist on the cost of hand weeding when weed densities are at or below the economic threshold.

Another important concept in weed management is the critical period (CP) of weed control. It is defined as the interval in the life cycle of the crop when it must be kept weed-free to prevent yield loss due to weed interference (Ross and Lembi, 1999;

Ohio Vegetable Production Guide, 2001; Martin et al., 2001). Critical periods vary widely depending on crop, weed species and densities, environmental conditions, and cultural practices, and are based on a yield loss of less than 5% due to weed interference.

Weeds emerging after the critical weed-free period will not affect yield. But, control efforts after this time may make harvest more efficient or reduce weed problems in subsequent years (OMAFRA, 2000). In this study, we use cabbage and processing tomato as our model systems for transitional organic vegetables. The critical weed free period for cabbage is 3 to 4 weeks (Horng, 1980; Miller, and Hoppen, 1991; Zimdahl,

2004) after planting, while for tomato it is 4 to 5 weeks after transplanting (Weaver and

Tan, 1983; Weaver, 1984). Using the critical weed free period will minimize the need 11

for season long cultivation and hand weeding. However, weeds that grow after the critical period will produce seed and reinfest future crops. In addition, weeds growing at harvest time may reduce crop quality and harvest efficiency (Ohio Vegetable Production

Guide, 2001).

Based on the above, we investigated the influence of nutrient and weed management techniques on weed emergence and weed seedbank properties in a transitional organic vegetable production system.

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CHAPTER 2

WEED MANAGEMENT STRATEGIES FOR TRANSITION TO ORGANIC:

THE CRITICAL PERIOD OF COMPETION AND THE NO SEED THRESHOLD

Karen Amisi, Douglas Doohan, Matthew Kleinhenz, Sally A. Miller, and Annette

Wszelaki

ABSTRACT

The best organic farmers rely on diverse opportunities to suppress weed populations throughout the complex rotations that characterize their farming systems.

Tactics include the rotation itself, tillage, cultivation, hand-weeding, living and plastic mulches, cover crops, and slashing. We investigated the use of two strategies, the critical period of competition (CP) and the no seed threshold (NST), and the effect of soil amendments (compost and manure) for farmers transitioning from conventional to organic production. Field experiments were conducted at the Ohio Agricultural Research and Development Center in Wooster, OH. In 2001, a 4-year rotation of wheat, clover, cabbage, and processing tomato transitioning to organic was established in soil previously in a conventional corn/soybean/forage agronomic rotation. The experimental design was a split plot in a randomized complete block design with 4 replications. Main 19

plots were soil amendments: none, raw dairy manure, and composted dairy manure.

Amendments were applied in spring at a rate equivalent to 101 kg N/ha and incorporated prior to planting. Subplots were weed control strategies: NST, where weed seedling were removed weekly for the whole season and no weeds were ever permitted to mature seeds in the field, and CP, where plots were kept weed free only for the first 5 weeks of crop growth. Each crop had 6 main plots of 222 m2 each and 24 subplots of 56 m2 each.

Evaluations included emerged weed communities both in the field and seedbank. A total of 30 and 40 weed species were identified from field plots and soil seedbank samples, respectively. NST weed management showed a decline in redroot pigweed and common lambsquarters density over time. Field emergence data showed that in 2002, redroot pigweed density was reduced by 32% and 37% in tomato NST plots 2 and 5 WAT, respectively. In 2003, redroot pigweed density was 61% and 49% lower 3 and 5 WAT, respectively, in NST than CP plots. Similarly, common lambsquarters density in NST plots was reduced by 51% and 59% at 3 and 5 WAT respectively, relative to CP plots.

Seedbank weed emergence data indicated that, in 2002 tomato, there were 93 and 90% fewer redroot pigweed and common lambsquarters seeds, respectively, in soil samples from NST plots than from CP plots. In 2003, redroot pigweed and common lambsquarter seeds were 63% and 71% lower in samples from cabbage NST plots than from CP plots.

Soil amendment effects on the density of redroot pigweed and common lambsquarters were not significantly different at P ≤ 0.05. However, occasional significant differences were noted between soil amendment and the two weed species though no clear trends were observed. Results from this study will support transitioning and existing organic farmers at the component, system and whole farm levels. 20

INTRODUCTION

The 1999 Organic Farmers Research survey reported that weeds were the top research priority in organic agriculture (OA) (Walz, 1999). In Ohio, 74.3% of organic growers responding to a state-wide survey ranked weed control as the major barrier to productivity. In addition, soil nutrient balancing and/or fertility without synthetic fertilizers were ranked as the second major barrier to productivity (Rzewnicki, 2000).

Weeds are particularly onerous during the transition from conventional agriculture to

OA (Petersen et al., 1999; Walz, 1999).

Organic farmers use many tactics to control weeds, including mechanical cultivation, hand-weeding or hoeing by hand, crop rotations, cover crops, mulches, planting date adjustment, row width adjustment, flaming, grazing by geese, ridge tillage, and solarization (Walz, 1999). Gaskell et al. (2000a) also lists other methods including water management, pre-germination of weeds, planting to moisture, and buried drip irrigation. Still other tactics with potential are microbial biocontrols (Kennedy and

Kremer, 1996), night tillage (Gallagher and Cardina, 1998), organic-compliant herbicides such as corn gluten (McDade and Christians, 2000), and cultivator-mounted computer guidance systems for distinguishing crop from weed (Smith et al., 2000).

The most successful organic farmers integrate as many tactics as possible, but rely primarily upon crop rotation and summer fallow (Nordell and Nordell, 1998, 2002).

Some have achieved relatively weed free conditions in which to grow crops. However, a recent unpublished survey of organic vegetable farmers in Ohio indicated that most did not practice an extensive crop rotation and relied primarily on plastic mulch to control weeds (Wszelaki and Doohan, 2003). Reliance on plastic has negative implications for 21

sustainability, because it is expensive, non-renewable, and may have undetermined negative effects that impact the soil biologically and environmentally. Plastic mulch presents a disposal problem for OA farmers and degrades soils quality. In contrast, the

OA literature (Liebman and Gallandt, 1997; Bond and Grundy, 2000; Liebman and

Davis, 2000; Lotter, 2003) indicates that weeds are best controlled through systemic management. Systemic weed management involves the whole cropping system

(Liebman and Davis, 2000) and integrates a wide range of cultural practices to promote biological diversity through rotations, cover cropping, organic amendments to stimulate soil biological activity, and the careful use of selected biological control techniques, naturally occurring plant extracts, and minerals (Lampkin, 1990).

Crop rotation is at the heart of the organic system, and is regarded as the cornerstone of weed, insect and disease management (Walz, 1999). However, few studies have closely examined the effects of crop rotation on weed dynamics, and in those few, crop rotation was often confounded with herbicide rotation, making it difficult to separate ecological from chemical effects. It is known that increasing crop diversity through rotation can reduce weed seed and plant density (Forcella and

Linsdtrom, 1988; Blackshaw, 1993; Martin and Felton, 1993) and prevent major shifts in weed community composition toward particularly aggressive or hard-to-control species.

These effects are due to the creation of complex, unstable patterns of resource availability, soil disturbance, and mechanical damage that reduce weed survival, growth and reproduction (Blackshaw, 1993; Martin and Felton, 1993). Seedling emergence and survival, weed growth and seed production are also affected by crop rotation. Thus,

carefully designed, timed, and intensively managed rotations are a common, integral part of weed, pest and disease management strategies in OA systems.

Animal manures and composts are important sources of nutrients on most organic farms, and can increase soil biological activity, improve soil structure and water holding capacity, and provide organic compounds that stimulate plant nutrient uptake and growth (Parr et al., 1986; Valdright et al., 1996). However, manure is a frequent source of weed seed introduction and dispersal in croplands (Mt. Pleasant and

Schalather, 1994).Compost, correctly made, should be free of weed seed. Thus management of manure and compost is important for both soil quality and weed dynamics (Gallandt et al., 1998). Farming practices that maintain or increase soil organic matter can be used to optimize soil microbial communities and activity, potentially to achieve weed suppression (Kremer and Kennedy, 1996; Gallandt et al., 1999; Kennedy,

1999; Kremer and Li, 2003). It is unknown if the addition of organic amendments like compost and manure may favor microbes that degrade weed seeds or attack weed seedlings (Kremer, 1993). The use of organic inputs may provide a cultural method to manage weeds, but if this is so, their effects on weeds must be better understood

(Fennimore and Jackson, 2003).

Because most organic farmers have already adopted a philosophy of systemic management and integration of multiple tactics, integrated pest management (IPM) may be particularly applicable. The IPM concepts of economic thresholds (ET) and critical period of competition (CP) are already strongly embedded within the weed management literature (Jones and Medd, 2000).

Cousens (1987) defined ET as “that weed density at which the cost of control measures equals the increased return in yield which could result”. In practice, fields are scouted for weeds after planting to guide weed management decisions, based upon the species encountered and their numbers (Norris, 1999). Crops in which single season ETs have been established include cereals, corn and soybean (Norris, 1999), alfafa (Medigo sativa L.) (Legere and Deschenes, 1989), onions (Allium cepa L.) (Dunan et al., 1995), sugarbeets (Beta vulgaris L.) (Norris, 1992), and tomatoes (Lycopersicon esculentum L.)

(Ackey et al., 1995). The ET concept is dependent on availability of tactics to control weed populations that will be present in the field each year (Norris, 1999).

The concept of CP is related to the concept of ET, and its discovery was an outgrowth of research aimed at quantifying and characterizing competition for resources between crops and weeds. The CP is defined as the time interval after crop seeding or transplanting when it is essential to maintain a weed-free environment in order to prevent crop yield loss (Swanton and Weise, 1991; Hall et al., 1992; Knezevic et al.,

2002; Zimdahl, 2004). In essence, the CP suggests that early weed control is almost always good compared to late weed control. The CP approach has sparked great interest because of the potential to reduce herbicide use by optimizing application timing, and especially, to reduce the prophylactic use of soil-active herbicides, and to ensure that weed control is based on biological necessity (Zimdhal, 1980; Weaver and Tan, 1983;

Weaver, 1984; Swanton and Wiese, 1991; Hall et al., 1992; Van Acker et al., 1993). The length of the CP varies depending upon the crop, weed(s) and environmental conditions, but typically ranges from 2 to 12 weeks after planting or transplanting for full season crops (Zimdahl, 2004). The CP for cabbage has been determined by Horng (1980) and 24

Miller and Hoppen (1991) to be 3 to 4 weeks after planting, while that for tomatoes has been determined by Weaver and Tan (1983) to be 4 to 5 weeks after transplanting.

Control of weeds after the CP is not necessary for optimum crop yields and should be valued only in terms of harvest efficiency (Swanton et al., 1998).

Significantly few farmers have adopted CP as a strategy to manage weed

(Gunsolus and Buhler, 1999) despite its apparent value. The CP may have limited value for many farmers because it is difficult to predict reliably. The environment plays a large part in regulating crop-weed competitive relationships and can influence the CP

(Lindquist et al., 1999). Generally the CP can be expected to vary somewhat with crop, cultural practices, location, season and weather conditions, soils, and weed species and their densities, making predictions for a particular situation difficult (Black et al., 1969;

Zimdahl, 1980, 1988; Hall et al., 1992; Van Acker et al., 1993; DiTomaso, 1995; Evans

2001; Halford et al., 2001; Knezevic, 2002). However, this concept may be of greater interest to organic farmers because of its potential to target limited weed control resources to the time when the greatest crop damage potential occurs and to minimize the cost of weed control.

The principal source of weed infestation in cropland is the soil weed seedbank, the reservoir of dormant seeds and seeds that are ready to germinate when environmental conditions are appropriate. Its size reflects past and present field management (Cavers and Benoit, 1989) and herein lies the greatest risk in using ET or CP as strategic management approaches. Both strategies are likely to compromise future weed control because of seed return from weeds that emerge after the CP or weeds that occur at densities below the ET (Swanton et al., 1998). If the input of additional seeds is 25

prevented or minimized, most viable seeds will be lost from the seedbank over time.

Organic farmers may benefit more from a focus on reducing the size of the weed seedbank than conventional growers because they have fewer tools at their disposal to control emerged weeds once the crop is established.

Seedbank management is an integral part of a long-term sustainable weed management system. One of the long-term weed strategies that can be adopted by farmers is the no seed threshold (NST) suggested by Norris (1995, 1999) and Jones and

Medd (2000). The NST is defined as a strategy where no weed seed production is ever permitted (Norris, 1995, 1999). The NST is predicted to result in a stepwise decline in the seedbank each time there is a germination event (Norris, 1999). However, in adopting the NST, organic farmers are bound to face an increase in their costs. The concept may be especially applicable to high value crops like vegetables in OA systems.

Norris (1999) argued that this increase in production costs would be offset by the reduction in weed populations in the future years.

In this research, we investigated and characterized the effects of weed management strategies (NST and CP) and soil amendments on weed densities and the weed seedbank during the transition period from conventional to organic. Our hypothesis was that the NST would result in a measurable reduction in the soil weed seedbank and weed seedlings over time.

MATERIALS AND METHODS

Field and greenhouse studies were conducted at the Ohio Agricultural Research and Development Center (OARDC), Wooster, Ohio from 2001 to 2004, latitude 400 47’

N and longitude 810 55’ W and of elevation 310 m.

Field weed emergence study

The field experiment consisted of 4 rotations designated as; Rotation 1 (Clover

2001,Tomato 2002, Cabbage 2003, and Wheat 2004); Rotation 2 (Tomato 2001,

Cabbage 2002, Wheat 2003, and Clover 2004); Rotation 3 (Cabbage 2001, Wheat 2002,

Clover 2003, and Tomato 2004); and Rotation 4 (Wheat 2001, Clover 2002, Tomato

2003, and Cabbage 2004). The following varieties and cultivars were used; processing tomatoes (Lycopersicon esculetum L.) cv ‘Peto 696’1, fresh market cabbage (Brassica oleraceae L.) cv ‘Bravo’2, winter wheat (Triticum aestivum L.) cv ‘Carl’, and red clover

(Trifolium pretense L.). Since the experiment was initiated in the spring, spring wheat was used in 2001 instead of winter wheat, which was used thereafter. Tomato and cabbage seeds were obtained locally, and were neither certified organic nor treated. The study was established in a field that was previously in a 3-year rotation of corn, soybean, and forage. In April 2001, prior to spring tillage and initiation of the transition, the entire area was sprayed with glyphosate at a rate of 1.0 kg/ha acid equivalent to eliminate perennial weeds.

The experimental design was a split plot in a randomized complete block with 4 replications. Plots were mold-board plowed and disc harrowed in April of each year.

Each crop in the rotation was designated to an area of 1338 m2 [55 m x 24.3 m]. The 27

main plot treatments each year in cabbage and tomato were the soil fertility amendments

– no amendment (control), raw dairy manure (hereon after referred to as manure), and composted dairy manure (hereon after referred to as compost). Soil amendments were not applied prior to planting clover or winter wheat. Manure and compost were applied to the cabbage and tomato fields in the spring (May 11, 14 and 18, 2001; April 18 and

19, 2002; May 15 and 19, 2003; and May 6, 2004) at rates determined to supply 101 kg

N/ha (Tables 2.1 and 2.2). Cabbage and tomato plots were immediately harrowed to incorporate the soil amendments prior to transplanting.

Tomato and cabbage transplants were seeded in the greenhouse on April 23,

2001, April 10, 2002, and April 15 and 22, 2003. In 2004, cabbage and tomatoes were not grown. Paygro organic potting mix # 423 (35% composted pine bark, 50% Canadian sphagnum peat, 15% perlite v/v/v)3, amended with 50 g m-2 Bradfield Eagle 3-1-5

Fertilizer4 was used. The seedlings were transplanted into the respective plots by June of each year (June 12 and 13, 2001; June 4 and 10, 2002; and June 17 and 18, 2003).

Winter wheat and red clover were seeded at the rate of 112 and 22 kg/ha, respectively, into the plots during the fall (October 30, 2001; September 10, 2002; and October 30,

2003). Amendments (main plots) were applied to the tomato and cabbage crops in 9.1 m wide strips (Figure 2.1). Each crop in the rotation had a total of 6 main plots, each with a size of 222 m2 [24.4 m wide x 54.9 m long] (2 reps of each amendment).

Subplot treatments were weed control strategies (Figure 2.2). The rotational sequence and main and subplot treatments were assigned to the field randomly. Weed management and soil amendment plots were designated for each crop in 2001, and the same weed management treatments were maintained throughout the duration of the 28

study. Every crop in the rotation had a total of 24 subplots, each with a size of 56 m2 [6.1 m wide x 9.1 m long].

Weed management tactics corresponded with standard practices used by local organic farmers. Tomato and cabbage plots designated as CP were maintained weed free by hand-weeding and hoeing for 5 weeks. The critical weed free period for cabbage is 3 to 4 weeks (Horng, 1980; Miller and Hoppen, 1991; Zimdahl, 2004) after planting, while for tomato it is 4 to 5 weeks after transplanting (Weaver and Tan, 1983; Weaver, 1984;

Zimdhal, 2004). Plots with NST treatments were kept weed free for the entire season; no weed was allowed to reach maturity and set seed. Tomato and cabbage were hoed and weeded by hand to remove any weeds that were present throughout the growing season.

NST plots in wheat stubble were sprayed with Burn Out5 (20% acetic acid) on

September 6, 2002, to control summer annual weeds that emerged after harvest. NST plots in clover were mowed on September 11, 2001, June 24 and August 28, 2002, June

25 and August 11, 2003, and June 24 and August 8, 2004 to control summer annual weeds. Weeds were not controlled in CP plots of either wheat or clover; however, clover was harvested twice each year, which provided some weed control.

Samples of soil, compost and manure for physical and chemical analysis and for determination of the weed seedbank were obtained from the field and stock piles, respectively, in April of each year. Soil samples were analyzed at the Service Testing and Research (STAR) Laboratory at OARDC for P, K, Ca, Mg, pH, soluble salts, total nitrogen, nitrate nitrogen, total carbon, and organic matter. Compost and manure samples were analyzed for pH, soluble salts, total solids (% moisture), volatile solids, total nitrogen, total carbon, major elements, ammonium nitrogen, and nitrate nitrogen. 29

Soil samples for quantifying the weed seedbank were stored in a cooler at 4 ºC until processed.

During the growing season, management practices like irrigation, disease and insect control were carried out as needed for tomato and cabbage. In 2001, overhead irrigation was applied on July 17 and 19 for 4 hours each date. In 2002, drip irrigation was applied on July 15, 22 and 26 for 6 hours each day, and on August 13 and 28 for 5 and 3 hours, respectively. In 2003, drip irrigation was applied on June 27 for 2 hours and August 21 for 2.5 hours. The tomato and cabbage fields were scouted for disease and insects. In 2002, Koicide 2000 (53% copper hydroxide)6 was applied to tomatoes to treat anthracnose (Colletotrichum coccodes), and bacterial spot (Xanthomonas capestris pv. vesicatoria). In 2003, Champion WP (77% copper hydroxide)7 was sprayed to treat anthracnose, septoria leaf spot (Septoria lycopersici), and early blight (Alternaria solani)on tomato. In 2001 and 2002, Dipel DF (54% Bacillus thuringiensis subsp. kurstaki)8 was used to manage cabbage insects. In 2003, Pyganic Crop Protection EC 1.4

(1.4% pyrethrins)9 and Dipel DF were sprayed alternately on both crops to manage insect pests.

Emerged weed seedlings in the cabbage and tomato fields were identified and counted in 3 quadrants (0.5 x 0.5 m)/subplot 2, 3, and 5 weeks after transplanting each crop. After counts were taken, each plot was weeded by hand. For the most part, only winter annuals emerged in winter wheat and clover. Because we were primarily interested in impacts upon summer annual species, data on emerged winter annuals were not recorded from wheat and clover plots. Data were recorded from wheat and clover on a few occasions (August 13, 2003 for wheat and May 30 and June 23, 2003 for clover) 30

when large amounts of summer annuals were observed. After the 5 initial weeks, only

NST plots were weeded thereafter. Tomatoes were harvested on September 9, 2001,

September 12, 2002 and September 22, 2003. Cabbages were harvested on September

25, 2001, and on September 16, in 2002 and 2003. Yield for both crops was recorded

(Tables 3.2 to 3.7). Weed control after tomato and cabbage harvest in 2001 was estimated visually on a scale of 0-9 and recorded as percentage, where 0-5 = < 60% poor control; 6 = 60-70% control; 7 = 70-80% control; 8 = 80-90% control; and 9 = 90-100% good / excellent control for the weed species present (Appendix Tables B1 and B2).

Estimates of redroot pigweed (Amaranthus retroflexus L.) seed production in CP plots immediately after tomato and cabbage harvest were done in 2002 (Appendix Table C1).

Weed seedbank study

(a) Estimating the viable seed in the weed seedbank using exhaustive germination.

The weed seedbank in each plot was quantified by exhaustive germination in the greenhouse. In April of each year, ten soil cores (3.5 cm x 15 cm) were taken from each subplot. In 2001 and 2002, soil cores were taken within a 2 m diameter circle in the center of each subplot. In 2003 and 2004, cores were taken along a diagonal transect 10 m long in each subplot. Samples from each plot were aggregated to form one composite sample per subplot. Each soil sample was sieved through a 6 mm screen to break up soil clods and remove plant debris or large stones.

Composite soil samples were spread 1.5 cm thick in 23 cm x 23 cm trays. Trays of soil were placed on greenhouse benches that were lined with capillary matting10. Soil

was moistened indirectly, by wetting the capillary matting beneath the trays, with tap water daily to facilitate seed germination. The greenhouse was set to a day / night temperature of 20/8 ºC and a natural photoperiod irradiance. Weed seedlings were identified and counted monthly, and pulled out once quantified. This cycle was repeated until no further weeds germinated. When weed emergence ceased, soil samples were stratified in a cooler at 4 0C for 4–6 weeks to break dormancy in any remaining seed.

The trays were returned to the greenhouse bench and the soil was stirred and moistened.

This procedure was repeated for 2 additional cycles to allow more weed seeds to germinate, until we observed no further weed germination.

(b) Characterization and identification of weed seeds in amendments.

In the spring of 2002 and 2003, samples of soil amendments were obtained by removing twenty 3.5 x 20 cm cores from the manure and compost stocks before they were incorporated into field plots. Samples were aggregated into four samples for each amendment, 5 cores/sample. Each composite sample of 5 cores was spread in trays 23 cm x 23 cm and placed on a greenhouse bench that was lined with capillary matting. The greenhouse environmental parameters were the same as those described above. Samples were moistened indirectly, by moistening the capillary matting, twice a week with tap water to facilitate weed emergence. Four additional samples of each amendment were mixed with Pro-Mix BX11 potting mix using a ratio of 3:1 (amendment:potting mix) and placed in trays.

Statistical analysis

Data on emerged weeds in tomato and cabbage in 2001 were summarized using 3 quantitative measures. Frequency, mean field uniformity, and mean field density were computed for each species using the method of Thomas (1985). Frequency indicates the percentage of plots infested by a species, and considers only the presence or absence of the weed in a plot. Mean field uniformity indicates the percentage of quadrants infested by a species and is an estimate of the area infested by the species. Mean field density indicates the number of plants m-2 and is used to indicate the magnitude of the infestation in the plot.

Frequency, mean field uniformity, and mean field density values for each species were combined into a single value called relative abundance (RA) as described by

Thomas (1985) (Appendix A). The RA value is used to rank the contribution of individual species in the weed community, and to compare contribution of groups of species to the community. It does not indicate the competitiveness of a weed. The total value for RA of all species in a community is 300 (Thomas et al., 1994). RA values for the weed seedbank study were calculated as above.

Weed density data from field and greenhouse studies were subjected to ANOVA at P ≤ 0.05 using PROC GLM (SAS version 8, 1999). All data met the assumptions of

ANOVA, and did not require transformation. No interactions were detected between weed treatments (CP and NST) and amendments (control, manure or compost).

RESULTS AND DISCUSSION

Field weed and weed seedbank seedling emergence

A total of 30 species were identified in the field and are listed in Table 2.3. All weeds present in the field plots were also present in the seedbank soil samples. The predominant species were summer annuals (60%), though some winter annuals (23%), biennials, simple and creeping perennials were present. RA for weed emergence data in

2001 is tabulated in Appendix Table A.1.

A total of 46 species identified from soil seedbank samples are listed in Table

2.3. Predominant species were summer annuals (70%), though winter annuals (23%), biennials, and perennials were present. A total of 29 weeds were ranked using the RA values (Appendix Tables A.2, A.3, A.4 and A.5).

Effect of weed management strategies on weed density

We report data for redroot pigweed (Amaranthus retroflexus) and common lambsquarter (Chenepodium album), since these were common in both the field plots and weed seedbank samples, appearing in at least two consecutive years and differing significantly among treatments. These species were also among the most abundant

(Appendix Table A.1). The average number of weeds per plot (density) is tabulated in

Tables 2.4 to 2.7. In 2004, vegetables were not grown; however, weed emergence was monitored.

Exhaustive germination of soil seedbank samples collected in spring 2001 indicated that redroot pigweed and common lambsquarters were uniformly distributed throughout the plots (Appendix Tables A.2, A.3, A.4, and A.5). As expected, 34

management strategies implemented in tomato and cabbage in 2001 did not affect emergence of redroot pigweed or common lambsquarter, except at 2 WAT, when redroot pigweed emergence was 33% less in tomato plots under the NST strategy (Table 2.5).

This observation may be related to patchy distribution of the species, although this is not supported by seedbank data from spring 2001 samples.

Field weed emergence: The NST strategy, as implemented in clover and tomatoes in 2001 (rotation 1 and 2), significantly impacted the density of redroot pigweed and common lambsquarters in tomato and cabbage in 2002 (Table 2.4 and 2.5).

Density of redroot pigweed was reduced by 32% in tomato NST plots 2 WAT and 37%

5 WAT (Table 2.4). Density at 3 WAT was not significantly different between weed management strategies. Common lambsquarter density in tomato was on average 57% lower in NST than in CP plots at each count, ranging from 53-64% (Table 2.4). Redroot pigweed density in cabbage was 22% lower 2 WAT in NST plots than in CP plots, but this was not significant at α = 0.05. Pigweed emergence did not occur between 2 and 3

WAT; however, 5 WAT 62% fewer redroot pigweed were observed in NST plots than in

CP plots (Table 2.5). A significant reduction (α = 0.05) in common lambsquarters was not detected in NST cabbage plots in 2002, though density was 33% and 62% lower than in CP plots at 2 and 3 WAT (Table 2.5).

Density of common lambsquarter and redroot pigweed in tomatoes in 2003

(rotation 4) was not affected by weed management in spring wheat during 2001 and clover in 2002 (Table 2.7). Few weeds emerged in spring wheat during 2001 due to dry weather after the late spring seeding. Likewise, few summer annuals grew in autumn

2001 following clover seeding in September. In contrast, weed management in the 35

previous year’s tomato crop profoundly affected weed density in cabbage in 2003

(rotation 1) (Table 2.4). Redroot pigweed density was 61% and 49% lower 3 and 5

WAT, respectively, in NST than in CP plots. Similarly, density of common lambsquarter in NST plots was reduced by 51% and 59% at 3 and 5 WAT, respectively, relative to density in CP plots.

Rainfall during summer 2002 was lower than the 30-year average (Appendix

Table D1), and few weeds were observed in winter wheat prior to harvest (data not reported). Common ragweed (Ambrosia artemisiifolia) and prostrate knotweed

(Polygonum aviculare) that emerged between wheat harvest and clover seeding were controlled with a spray of 20% acetic acid5 in NST plots. Fewer redroot pigweed were observed in NST than in CP clover plots in 2003 (rotation 3), and this was significant at

5 WAT (Table 2.6). This effect was most likely related to season-long weed control in cabbage in 2001, rather than to spraying of acetic acid in wheat the previous year.

Vegetables were not grown in 2004, but weed emergence was monitored in plots where the crop would have been planted. Fewer weeds emerged in 2004 in NST plots than in CP plots (rotations 3 and 4) (Tables 2.6 and 2.7); however, this was not always significant. Common lambsquarters was largely absent in the field during 2004, detected only 2 WAT in what would have been cabbage plots in 2004 (Table 2.7). Emergence of redroot pigweed was, on average, 60% lower in NST than in CP plots, and this was significant 3 WAT (Table 2.7) in what would have been cabbage plots in 2004. Redroot pigweed did not emerge 2 WAT in what would have been tomato plots in 2004, and the lower number observed in NST plots 3 WAT was not significant (Table 2.6). However,

5 WAT 51% fewer redroot pigweed seedlings were observed in NST plots than in CP 36

plots. Common lambsquarters did not emerge in what would have been tomato plots during 2004 (Table 2.6). This observation may be related to cumulative effects of weed control in cabbage in 2001 and in wheat and clover in 2002 and 2003, respectively.

However, common lambsquarters seeds were detected in seedbank samples drawn in

April 2004 (Table 2.8), and the literature indicates that seeds of this species can persist in soil for several decades (Toole and Brown, 1946; Lewis 1973). Redroot pigweed density in cabbage plots was 41% lower in NST than CP plots at 2 WAT, though this was not significant (α = 0.05) (Table 2.7). At 3 WAT, 87% fewer redroot pigweeds were observed in NST than in CP plots. A significant reduction (α = 0.05) in common lambsquarters was not detected in NST cabbage plots in 2004, though density was 30% lower than in CP plots at 2 WAT. Common lambsquarters did not emerge 3 and 5 WAT in 2004, suggesting that weed management strategies in tomatoes in 2001 and 2003 were effective in depleting the seedbank.

Seedbank weed emergence: Seedling emergence counts from seedbank samples were converted to seedling density/m2 based on a 3.5 cm sample core diameter (Table

2.8). Significant differences in redroot pigweed and common lambsquarters were not detected in the spring of 2001, indicating that populations were distributed evenly throughout the field when the study was initiated. In 2002 tomato (rotation 1), there were

93% and 90% fewer redroot pigweed and common lambsquarters seeds, respectively, in soil samples from NST plots than from CP plots. These species attained very high numbers in clover seeded in May 2001 (data not recorded). However, all weeds and clover were harvested in NST plots and removed from the field on September 11, 2001, setting up a large differential in seed rain between the weed management strategies as 37

reflected in spring 2002 soil seedbank samples and in the number of individuals that emerged in tomatoes in 2002. Likewise, in 2002 cabbage (rotation 2), the impact of NST and CP strategies in tomato in 2001 was apparent in the number of redroot pigweed seeds in soil samples collected in spring 2002. Data for common lambsquarters were not significant for weed management strategy.

The lesser impact of weed management strategies in 2001 tomato (rotation 2) in comparison to 2001 clover (rotation 1) was due to a relatively high degree of weed control obtained in CP tomato plots, whereas no control was practiced in CP clover plots

(Table 2.8). Weed control in cabbage in 2001 (rotation 3) did not affect pigweed and lambsquarters seed deposition according to analysis of seedbank samples collected in spring 2002. As expected, no differences were detected in seed content of seedbank samples collected in 2002 clover plots (rotation 4) because weed management strategies were not applied in spring wheat in 2001. Fewer weed seeds in soil samples collected in spring 2003 and 2004 in cabbage and wheat plots, respectively, further demonstrated the effect of NST on seedbank populations. Redroot pigweed and common lambsquarters were 63% and 71% fewer in samples from cabbage NST plots than in samples from CP plots, reflecting high levels of weed control and prevention of weed seed production in clover in 2001 and tomato in 2002. The impact was also apparent on lambsquarters in samples from wheat in 2004, although data for pigweed were not significant.

Data from wheat and clover plots sampled in 2003 and 2004, respectively, failed to reflect a significant effect of the weed management strategies used in tomato in 2001 and cabbage in 2002 (Table 2.8). However, seed numbers declined more or less in stepwise fashion, as few weeds survived in cabbage in 2002, regardless of strategy, 38

because of dry summer weather and because of survival of very few weeds in winter wheat in 2003.

Weed management in Rotations 3 and 4 had the least effect on weed seed in soil samples (Table 2.8). Seed number of redroot pigweed and common lambsquarters in wheat in 2002 (Rotation 3) were reduced by approximately 24%; however, seed number did not differ significantly between the two strategies. Summer annual weeds (common ragweed and prostrate knotweed) were controlled in wheat NST plots by spraying acetic acid, but this treatment had no effect on pigweed and lambsquarters seeds buried in the soil. This explains the lack of differences in weed seedbank numbers in 2003 clover and

2004 tomato. In Rotation 4, weed management strategies were not applied in spring wheat in 2001. Even though NST plots in clover were mowed twice in 2002, the small number of summer annual weeds removed did not create a detectable difference in lambsquarters and pigweed in the seedbank in tomato in spring 2003. Seed number did decline over time with this rotation, because of the few weeds that produced seeds during the wheat and clover sequences. Weed control strategies in tomatoes in 2003 did not affect seed number in soil samples collected in spring of 2004 (Table 2.8), but did affect the number of emerged weeds counted in the plots (Table 2.7).

Effect of soil amendments on weed density

Generally, the effect of soil amendments (control [no amendment], compost and manure) on the density of redroot pigweed and common lambsquarters was not significantly different at P ≤ 0.05. However, in some cases significant differences were noted between soil amendments though no clear trends were observed. 39

Field weed emergence: Soil amendments significantly impacted the density of redroot pigweed in tomato 2002 (rotation 1) (Table 2.9). At 3 WAT, density of redroot pigweed in control plots was 35% and 41% more than in manure and compost amended plots respectively. At 5 WAT, redroot pigweed density in manure amended plots was

20% and 49% more than in the control and compost amended plots respectively

In cabbage 2002 (rotation 2), redroot pigweed density at 2 WAT was 43% more in compost amended plots than in manure amended plots (Table 2.10). In cabbage 2001

(rotation 3), redroot pigweed density at 2 WAT was 65% more in compost amended plots than in manure amended plots (Table 2.11). However in tomato 2004 (rotation 3), redroot pigweed density in manure amended plots at 3 WAT was 28% and 72% greater than in the compost amended or control plots respectively (Table 2.11).

Soil amendments did not significantly impact common lambsquarters density in rotations 1, 2 and 3. However, in cabbage 2004 (rotation 4), common lambsquarters density in manure amended plots at 2 WAT was 44% and 67% greater than in compost amended or control plots respectively (Table 2.12).

Seedbank weed emergence: Soil amendments impacted weed density for both weed species in rotations 1 and 2. In tomato 2002 (rotation 1), common lambsquarters density in compost amended plots was 41% and 86% more than in control and manure amended plots respectively. However, for cabbage 2003 (rotation1), lambsquarter density in control plots was 42% and 72% more than in compost and manure amended plots respectively. In tomato 2001 (rotation 2), redroot pigweed density in manure amended plots was 47% and 80% greater than in the control and compost amended plots respectively. However for cabbage 2002 (rotation 2), common lambsquarter density in 40

compost amend plots was 14% and 40% greater than in control and manure amended plots respectively.

Identification of weed seed in compost and manure samples

No weed seedlings emerged from the manure or compost samples that were collected in 2002 and 2003. This suggests that the manure or compost did not have any weed seed, or if they did, then the seed was dormant. This does not agree with a previous report in the literature, which states that manure and compost are often sources of weed introduction and dispersal in croplands (Mt. Pleasant and Schalather, 1994). However, it is possible and likely that the food sources provided to cattle at the OARDC dairy facility were free of weed seeds, leading, therefore, to manure and ultimately compost that did not contain weed seeds.

CONCLUSION

By and large, data from both the field and seedbank emergence agree with the prediction that use of NST leads to a stepwise decline in the weed seedbank (Norris,

1999). NST weed management showed a decline in redroot pigweed and common lambsquarters density over time. The CP treatment almost always had greater numbers of weeds compared to the NST treatment. These data support our hypothesis that the adoption of NST resulted in a reduction of weeds. However, more research needs to be done to validate our results.

Soil amendment effects on weed density though significant in some cases, did not indicate a clear trend. Thus it was difficult to explain amendment effects. When developing weed management strategies for organic vegetable production systems, the management of organic matter, soil nutrients and soil microbial biomass needs to be considered. Therefore, further work must also be undertaken to understand better the interactions between weed emergence and organic amendments in organic vegetable production systems.

SOURCE OF MATERIALS

1. Seminis Vegetables Seeds, Oxnard, California.

2. Harris Seeds, Rochester, New York.

3. Paygro Co. Garrick Industries, South Charleston, Ohio.

4. Bradfield Industries, Inc., Springfield, Missouri.

5. St. Gabriels Laboratories, Gainesville, Virginia.

6. Griffen L.L.C., Valdosta, Georgia.

7. Agritol International, Houston, Texas.

8. Valent Biosciences Corporation, Libertyville, Illinois.

9. McLaughlin Gormley King Company, Golden Valley, Minnesota.

10. Hummert International, Earth City, Missouri.

11. Burton Flower and Garden Supply Company, Burton, Ohio.

EXPERIMENTAL PLOT PLAN

LOCATION OF AMENDMENT APPLICATIONS

DAIRY COMPLEX

< NORTH OIL CITY ROAD

(1) SPRING WHEAT (3) PROCESSING TOMATO

123456252627282930

7 8 9 10 11 12 31 32 33 34 35 36

43 13 14 15 16 17 18 37 38 39 40 41 42

19 20 21 22 23 24 43 44 45 46 47 48 ACCESS ROAD

(2) RED-CLOVER (4) FRESH MARKET CABBAGE

* Plot rows will run north-south (parallel to Oil City Road). Each experimental unit measures 6.1 m wide (east-west) x 9.1 m long (north-south).

Plot and Amendment (2001) 1-12 = none 28, 34 = compost 39, 55 = none 13-24 = none 29, 35 = manure 40, 46 = none 25, 31 = manure 30, 36 = none 41, 47 = compost 26, 32 = none 37, 43 = compost 42, 48 = manure 27, 33 = compost 38, 44 = manure

Figure 2.1: Plot map showing location of soil amendments in 2001 12.

IFAFS 2000 VEGETABLE-GRAIN TRANSITION PLOT MAP -- 2001 (updated 6/12/01)

LOCATION OF WEED TREATMENTS DAIRY COMPLEX

< NORTH OIL CITY ROAD (1) SPRING WHEAT (3) PROCESSING TOMATO

1E 2E 3E 4E 5E 6E 25E 26E 27E 28E 29E 30E 1W 2W 3W 4W 5W 6W 25W 26W 27W 28W 29W 30W 7E 8E 9E 10E 11E 12E 31E 32E 33E 34E 35E 36E 7W 8W 9W 10W 11W 12W 31W 32W 33W 34W 35W 36W 13E 14E 15E 16E 17E 18E 37E 38E 39E 40E 41E 42E 13W 14W 15W 16W 17W 18W 37W 38W 39W 40W 41W 42W ACCESS ROAD

44 19E 20E 21E 22E 23E 24E 43E 44E 45E 46E 47E 48E 19W 20W 21W 22W 23W 24W 43W 44W 45W 46W 47W 48W

(2) RED-CLOVER (4) FRESH MARKET CABBAGE

* Plot rows will run north-south (parallel to Oil City Road). Each experimental unit measures 6.1 m wide (east-west) x 9.1 m long (north-south).

Plot and Weed Treatments (2001) E = East NST = No Seed Threshold W = West CP = Critical Period

1E, 2W, 3E = CP 4W, 5E, 6E = CP 25W, 26E, 27E = CP 28W, 29E, 30W = CP 1W, 2E, 3W = NST 4E, 5W, 6W = NST 25E, 26W, 27W = NST 28E, 29W, 30E = NST 7W, 8W, 9E = CP 10E, 11W, 12E = CP 31E, 32W, 33E = CP 34W, 35W, 36E = CP 7E, 8E, 9W = NST 10W, 11E, 12W = NST 31W, 32E, 33W = NST 34E, 35E, 36W = NST

13W, 14W, 15E = CP 16E, 17W, 18E = CP 37E, 38W, 39W = CP 40E, 41E, 42W = CP 13E, 14E, 15W = NST 16W, 17E, 18W = NST 37W, 38E, 39E = NST 40W, 41W, 42E = NST 19E,20E, 21W = CP 22E, 23W, 24E = CP 43E, 44W, 45E = CP 46W, 47W, 48E = CP 19W, 20W, 21E = NST 22W, 23E, 24W = NST 43W, 44E, 45W = NST 46E, 47E, 48W = NST

13.Fig ure 2.2: Plot map showing location of weed treatments in 2001

Characteristics pH Moisture Total Total N P K Amount Total Year % C % % % applied N (by wt.) % (by wt.) (by wt.) (by wt.) kg/ha kg/ha 2001 7.95 50 31.3 1.3-1.5 0.7 1.5 37868 100.8 2002 8.42 50 42.2 1.5 0.2 1.1 34050 100.8 2003 7.97 64 42.0 1.3 0.3 1.2 38487 100.8 2004 7.67 81 42.7 0.7 0.2 0.6 69132 100.8

Characteristics Moisture Total N P K Amount Total

% Total C % % % applied N Year pH (by wt.) % (by wt) (by wt.) (by wt.) kg/ha kg/ha 2001 8.53 65 45.4 0.5 0.1 0.7 41376 100.8 2002 8.81 75 44.4 0.8 0.1 0.6 25073 100.8 2003 8.47 71 47.6 0.4 0.1 0.7 49527 100.8 2004 7.83 74 49.2 0.4 0.1 0.2 50045 100.8

Bayer Seed Code Field bank Scientific name Family Common Name Life Cycle plots samples ABUTH Abutilon theophrasti Medicus Malvaceae velvetleaf SA NP P AMARE Amaranthus retroflexus L. Amaranthaceae pigweed, redroot SA P P AMBEL Ambrosia artemisiifolia L. Compositae ragweed, common SA P P BARVU Barbarea vulgaris R. Br. Cruciferae rocket, yellow WA, B, SP NP P CAPBP Capsella bursa-pastoris (L.) Medicus Cruciferae shepherd's-purse WA, SA P P CERVU Cerastium vulgatum L. Caryophyllaceae chickweed, mouseear SP NP P CHEAL Chenopodium album L. Chenopodiaceae lambsquarters,common SA P P CIRAR Cirsium arvense (L.) Scop. Compositae thistle, Canada CP P P CIRVU Cirsium vulgare (Savi) Tenore Compositae thistle, bull B P P CONAR Convolvulus arvensis L. Convolvulaceae bindweed, field CP P P

46 CYPES Cyperus esculentus L. Cyperaceae nutsedge, yellow CP P P DAUCA Daucus carota L. Umbelliferae carrot, wild B NP P DIGSA Digitaria sanguinalis (L.) Scop. Gramineae crabgrass, large SA P P ECHCG Echinochloa crus-galli (L.) Beauv. Gramineae barnyardgrass SA P P ERICA Conyza canadensis (L.) Cronq. Compositae horseweed SA, WA, B P P GASCI Galinsoga ciliata (Raf.) Blake Compositae galinsoga, hairy SA NP P GASPA Galinsoga parviflora Cav. Compositae galinsoga, smallflower SA P P IPOHE Ipomoea hederacea (L.) Jacq. Convolvulaceae morningglory, ivyleaf SA P P LACSE Lactuca serriola L. Compositae lettuce, prickly B NP P LAMAM Lamium amplexicaule L. Labiatae henbit WA P P

LAMPU Lamium purpureum L. Labiatae deadnettle, purple WA NP P MALNE Malva neglecta Wallr. Malvaceae mallow, common WA,SA,B P P MELAL Silene alba (Mill.) E.H.L.Krause Caryophyllaceae campion, white WA,SA,B,SP NP P MEDLU Medicago lupulina L. Leguminosae medic, black SP,B,SA NP P MOLVE Mollugo verticillata L. Aizoaceae carpetweed SA NP P OXAST Oxalis stricta L. Oxalidaceae woodsorrel, yellow SA,SP P P PHBPU Ipomoea purpurea (L.) Roth Convolvulaceae morningglory, tall SA NP P PLAMA Plantago major L. Plantaginaceae plantain, broadleaf SP P P POAAN Poa annua L. Gramineae bluegrass, annual WA,SA NP P POLAV Polygonum aviculare L. Polygonaceae knotweed, prostrate SA P P POLCO Polygonum convolvulus L. Polygonaceae buckwheat, wild SA P P POLPY Polygonum pensylvanicum L. Polygonaceae smartweed,Pennsylvania SA P P POROL Portulaca oleracea L. Portulacaceae purslane, common SA P P

47 RUMAA Rumex acetosella L. Polygonaceae sorrel, red CP NP P RUMCR Rumex crispus L. Polygonaceae dock, curly SP P P SETLU Setaria glauca (L.) Beauv. Gramineae foxtail, yellow SA NP P SETVI Setaria viridis (L.) Beauv. Gramineae foxtail, green SA P P SIDSP Sida spinosa L. Malvaceae sida, prickly SA NP P SINAR Brassica kaber (DC.) L.C.Wheeler Cruciferae mustard, wild SA P P SOLPT Solanum ptycanthum Dun. Solanaceae nightshade,easternblack SA P P SONOL Sonchus oleraceus L. Compositae sowthistle, annual SA NP P STEME Stellaria media (L.) Vill. Caryophyllaceae chickweed, common WA P P TAROF Taraxacum officinale Weber in Wiggs Compositae dandelion SP P P THLAR Thlaspi arvense L. Cruciferae pennycress, field WA P P TRFRE Trifolium repens L. Leguminosae clover, white CP P P VERPG Veronica peregonia L. Scrophulariaceae Speedwell, purslane WA P P

Table 2.3 continued

AMARE CHEAL Rotation sequence WAT CP NST CP NST Rotation 1 2 - - - - Clover 2001 3 - - - - 5 - - - - Total - - - -

2 1610 a 1087 b 2153 a 1002 b Tomato 2002 3 691 604 398 a 143 b 5 915 a 579 b 380 a 174 b Total 3216 2270 2931 1319

2 NP NP NP NP Cabbage 2003 3 3061 a 1207 b 1655 a 803 b 5 1587 a 809 b 1767 a 728 b Total 4648 2016 3422 1531

2 NP NP 882 311 Wheat 2004 3 NP NP NP NP 5 NP NP NP NP Total NP NP 882 311

Table 2.4: The effect of weed management strategies (CP and NST) on average number of redroot pigweed (AMARE) and common lambsquarters (CHEAL) seedlings / plot (56 m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 1. For both AMARE and CHEAL: NP = weed not present at the time of counting; dash ( - ) = no data; Total = total number of weeds counted for 2, 3, and 5 WAT for each rotation sequence. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns.

AMARE CHEAL Rotation sequence WAT CP NST CP NST Rotation 2 2 403 a 272 b 120 165 Tomato 2001 3 NP2 NP NP NP 5 NP NP NP NP Total 403 272 120 165

2 4300 3348 417 280 Cabbage 2002 3 NP NP NP NP 5 554 a 212 b 181 69 Total 4854 3560 598 349

2 - - - - Wheat 2003 3 - - - - 5 NP NP 11 4 Total NP NP 11 4

2 NP NP NP NP Clover 2004 3 NP NP NP NP 5 NP NP NP NP Total NP NP NP NP

Table 2.5: The effect of weed management strategies (CP and NST) on average number of redroot pigweed (AMARE) and common lambsquarters (CHEAL) seedlings / plot (56 m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 2. For both AMARE and CHEAL: NP = weed not present at the time of counting; dash ( - ) = no data; Total= total number of weeds counted for 2, 3, and 5 WAT for each rotation sequence. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns.

AMARE CHEAL Rotation sequence WAT CP NST CP NST Rotation 3 2 793 473 274 397 Cabbage 2001 3 NP NP NP2 NP 5 NP NP NP NP Total 793 473 274 397

2 - - - - Wheat 2002 3 - - - - 5 - - - - Total - - - -

2 24 19 17 16 Clover 2003 3 - - - - 5 4 a 1 b 20 16 Total 28 20 37 32

2 NP NP NP NP Tomato 20045 3 1244 622 NP NP 5 1659 a 822 b NP NP Total 2903 1444 NP NP

Table 2.6: The effect of weed management strategies (CP and NST) on average number of redroot pigweed (AMARE) and common lambsquarters (CHEAL) seedlings / plot (56 m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 3. For both AMARE and CHEAL: NP = weed not present at the time of counting; dash ( - ) = no data; Total= total number of weeds counted for 2, 3, and 5 WAT for each rotation sequence. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns.

AMARE CHEAL Rotation sequence WAT CP NST CP NST Rotation 4 2 - - - - Wheat 2001 3 - - - - 5 - - - - Total - - - -

2 - - - - Clover 2002 3 - - - - 5 - - - - Total - - - -

2 840 753 355 454 Tomato 2003 3 NP NP NP NP 5 678 678 641 579 Total 1518 1431 996 1033

2 1141 674 519 363 Cabbage 2004 3 778 a 104 b NP NP 5 NP NP NP NP Total 1919 778 519 363

Table 2.7: The effect of weed management strategies (CP and NST) on average number of redroot pigweed (AMARE) and common lambsquarters (CHEAL) seedlings / plot (56 m2) 2, 3, and 5 weeks after transplanting (WAT) for Rotation 4. For both AMARE and CHEAL: NP = weed not present at the time of counting; dash ( - ) = no data; Total= total number of weeds counted for 2, 3, and 5 WAT for each rotation sequence. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species columns.

Seedbank Rotation Sequence AMARE CHEAL CP NST CP NST Rotation 1 Clover 2001 5729 4284 1191 558 Tomato 2002 14221 a 989 b 4588 a 431 b Cabbage 2003 1166 a 431 b 2864 a 837 b Wheat 2004 380 228 2738 a 760 b Rotation 2 Tomato 2001 8289 4715 1192 1952 Cabbage 2002 2941 a 1622 b 1191 1242 Wheat 2003 3473 1445 837 634 Clover 2004 355 253 456 507 Rotation 3 Cabbage 2001 5070 4715 1749 1420 Wheat 2002 2636 2002 1191 913 Clover 2003 837 1293 1952 887 Tomato 2004 355 355 1369 659 Rotation 4 Wheat 2001 3523 2307 1293 1420 Clover 2002 1242 1825 811 608 Tomato 2003 177 177 862 659 Cabbage 2004 253 304 456 152

Table 2.8: The effect of weed management strategies on average number of emerged redroot pigweed (AMARE) and common lambsquarters (CHEAL) / plot (56 m2) from soil seedbank samples for Rotations 1, 2, 3 and 4. Means followed by different letters within each row are significantly different at P ≤ 0.05 within weed species.

AMARE CHEAL Rotation Sequence WAT Control Compost Manure Control Compost Manure

Rotation 1 2 ------Clover 2001 3 ------5 ------Total ------

2 1750 1372 924 1559 155 1419 Tomato 2002 3 868 a 513 b 560 b 317 308 187 5 775 ab 495 b 971 a 224 299 308 Total 3393 2380 2455 2100 2362 1914

53 2 NP NP NP NP NP NP Cabbage 2003 3 2511 1521 2371 1185 1493 1008 5 1279 1045 1269 1195 1428 1120 Total 3790 2566 3640 2380 2921 2128

2 ------Wheat 2004 3 ------5 ------Total ------

AMARE CHEAL Rotation Sequence WAT Control Compost Manure Control Compost Manure

Rotation 2 2 438 343 231 145 231 51 Tomato 2001 3 NP NP NP NP NP NP 5 NP NP NP NP NP NP Total 438 343 231 145 231 51

2 4452 a 4461 a 2557 b 327 485 233 Cabbage 2002 3 NP NP NP NP NP NP 5 373 364 411 84 121 168 Total 4825 4825 2968 411 606 401

54 2 ------Wheat 2003 3 ------5 ------Total ------

2 ------Clover 2004 3 ------5 ------Total ------

AMARE CHEAL Rotation Sequence WAT Control Compost Manure Control Compost Manure

Rotation 3 2 446 b 1078 a 375 b 446 284 277 Cabbage 2001 3 NP NP NP NP NP NP 5 NP NP NP NP NP NP Total 446 1078 375 446 284 277

2 ------Wheat 2002 3 ------5 ------Total ------

55 2 ------Clover 2003 3 ------5 ------Total ------

2 NP NP NP NP NP NP Tomato 2004 3 389 b 1011 ab 1400 a NP NP NP 5 1556 1167 1089 NP NP NP Total 1945 2178 2489 NP NP NP

AMARE CHEAL Rotation Sequence WAT Control Compost Manure Control Compost Manure

Rotation 4 2 ------Wheat 2001 3 ------5 ------Total ------

2 ------Clover 2002 3 ------5 ------Total ------

56 2 952 560 877 439 401 373 Tomato 2003 3 NP NP NP NP NP NP 5 775 467 793 653 607 569 Total 1727 1027 1670 1092 1008 942

2 1167 856 700 233 c 389 b 700 a Cabbage 2004 3 544 311 467 NP NP NP 5 NP NP NP NP NP NP Total 1711 2878 1167 233 389 700

AMARE CHEAL Rotation Sequence Control Compost Manure Control Compost Manure Rotation 1 Clover 2001 2662 5856 6502 608 1027 989 Tomato 2002 7643 6578 8593 1597 b 2700 a 418 c Cabbage 2003 837 304 1255 3080 a 1787 a 837 b Wheat 2004 190 228 494 1369 2586 1293 Rotation 2 Tomato 2001 5971 ab 2245 b 1129 a 3042 3574 913 Cabbage 2002 2738 1977 2129 1637 ab 1901 a 1255 b Wheat 2003 2091 2966 2357 570 1787 342

57 Clover 2004 ------Rotation 3 Cabbage 2001 1789 6996 5895 1179 1331 2243 Wheat 2002 1825 2395 2738 1331 989 837 Clover 2003 ------Tomato 2004 304 266 494 1369 837 837 Rotation 4 Wheat 2001 2281 3536 2928 1559 1483 1027 Clover 2002 1369 2015 1217 951 380 799 Tomato 2003 266 76 190 1065 875 494 Cabbage 2004 380 304 152 532 76 304

Table 2.13: The effect of soil amendment (control, compost, and manure) on average number of emerged redroot pigweed (AMARE) and common lambsquarters (CHEAL) seedlings / plot (56m2) from soil seed bank samples for Rotations 1, 2, 3, and 4. For AMARE and CHEAL: dash (-) = no data for clover. Means followed by different letters within each row are significantly different at P ≤ 0.05, within weed species column.

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CHAPTER 3

ECONOMICS OF NO SEED THRESHOLD WEED MANAGEMENT AND SOIL

AMENDMENTS IN ORGANIC TOMATO AND CABBAGE

Karen Amisi, Douglas Doohan, Matthew Kleinhenz, Sally A. Miller, and Annette

Wszelaki.

ABSTRACT

We determined the labor required to implement the no seed threshold (NST) and critical period of competition (CP) weed management strategies in a four year rotation of wheat, clover, tomato, and cabbage transitioning from conventional to organic production. Field studies were conducted at the Ohio Agricultural Research and

Development Center Wooster, Ohio from 2001 to 2004. Weed management tactics included mowing and harvesting in clover, acetic acid spraying in winter wheat, hand weeding and cultivation in cabbage and tomato. Hand weeding was carried out in all

NST plots for the entire growing season of the tomato and cabbage crops. Critical period plots were weeded for 5 weeks. Time to hand-weed was recorded and the labor cost of each strategy was computed. Yield and quality of tomato and cabbage were determined

each year to study the impact of weed management systems on these parameters. We report on the labor required by the two weed management strategies and their effects on tomato and cabbage yield. In 2002, NST and CP plots required 21.3 and 23 hours respectively to weed for 5 weeks. However, an additional 21.1 hours were required to weed NST plots in tomato for the entire season. In 2003, 33% more labor was required to keep plots weed free in NST than in CP. Labor costs ranged from an average of

$192/ha for CP to $296/ha for NST. Results indicate that the NST weed management strategy took longer and is more expensive to achieve compared to CP. In the long-term, as the weed population decreases, less time will be taken to achieve NST. In addition, the labor costs incurred will be reduced.

INTRODUCTION

The 1999 Organic Farmers Research survey reported that weeds were a research priority in organic agriculture (OA) (Walz, 1999). In Ohio, 74.3 % of organic growers responding to a state-wide survey, ranked weed control as the major concern or barrier to productivity (Rzewnicki, 2000). Weeds limit crop yield by competing for nutrients, water and light and may interfere with harvest. Inputs and labor associated with weed control are major budget items in production of organic produce.

In OA, weeds are best controlled through systemic management. Systemic management integrates rotations, mixed and cover cropping, organic amendments to stimulate soil biological activity, naturally occurring plant extracts, minerals and the careful use of control techniques (Lampkin, 1990; Liebman and Davis, 2000). Crop

rotation is central to the organic system. The method and timing of soil cultivation, and the choice of crop both contribute in different ways to manipulation of the weed population (Bond and Grundy, 2000). Animal manures and composts, important sources of nutrients on most organic farms, are often sources of weed seed (Mt. Pleasant and

Schalather, 1994). Thus management of manure and compost is important for both soil quality and weed dynamics (Gallandt et al., 1998).

Weed management tactics used in OA include mechanical cultivation, hand- weeding or hoeing by hand, crop rotations, cover crops, mulches, planting date adjustment, row width adjustment, flaming, grazing by geese, ridge tillage, solarization, water management, pre-germination of weeds, planting to moisture, and buried drip irrigation (Walz, 1999; Gaskell et al., 2000a). The most successful organic farmers integrate as many of these as possible, but rely primarily upon crop rotation, summer fallow, mechanical cultivation, weeding by hand, and hoeing (Nordell and Nordell,

1998, 2002). Economic thresholds (ET) and critical period of competition (CP) strategies are additional approaches of potential use to manage weeds in OA systems. These strategies are grounded in ecological concepts and are underpinned by a foundation of experimental data.

Cousens (1987) defined ET as “that weed density at which the cost of control measures equals the increased return in yield which could result”. Researchers have attempted to establish single season ETs for many crops including soybean, maize, cereal grains, alfalfa (Medigo sativa L.), onions (Allium cepa L.), sugarbeets (Beta

vulgaris L.), and tomatoes (Lycopersicon esculentum L.) (Legere and Deschenes, 1989;

Norris, 1992; Ackey et al., 1995; Dunan et al., 1995; Norris 1999).

The CP refers to the period following crop planting when weeds must be controlled to prevent loss of crop yield and / or quality (Swanton and Weise, 1991; Hall et al., 1992; Knezevic et al., 2002; Zimdahl 2004). The CP strategy may be of great use to organic farmers, because of its potential to target weed control resources to the time when the greatest crop damage potential occurs and to minimize the cost of weed control. The CP concept suggests that early weed control is almost always good compared to late weed control. Weed control after the CP is not necessary for optimum crop yields (Swanton et al., 1999).

Drawbacks that limit application of CP and ET have been summarized elsewhere, and to date relatively few farmers have adopted them as guiding principles of weed management (Gunsolus and Buhler 1999, Norris 1999; Amisi, 2005). The major concern about any strategy that permits certain weeds to grow is that weed control in future years will be compromised by allowing the current weeds to contribute to the soil weed seedbank (Swanton et al., 1998). This may occur from weeds that emerge after the critical period or from uncontrolled weeds that occur at densities below the ET (Swanton et al., 1999).

Organic farmers may benefit more from a focus on reducing the size of the weed seedbank, than would conventional growers, because they have fewer tools at their disposal to control emerged weeds once the crop is established. Seed survival has a greater influence on population dynamics than plant survival, and arguably management

aimed at enhancing mortality of buried weed seeds (like repeated cultivation) is more effective than management aimed only at killing weed seedlings (Jordan et al., 1995).

One of the long-term weed management strategies that could be adopted by organic farmers is the No Seed Threshold (NST) suggested by Norris (1995, 1999) and Jones and Medd (2000).

In NST, weeds are destroyed as needed to prevent seed production (Norris 1995,

1999). The NST concept may be especially applicable to high value crops like organic vegetables. The use of NST is predicted to result in a stepwise decline in the seedbank each time there is a germination event (Norris, 1999). However, in adopting the NST organic farmers are bound to face an increase in costs. Norris (1999) argued that this increase in production costs would be offset by reduction in weed populations in future years.

We investigated the effects of the NST and CP approach on soil weed seedbanks in a four year rotation of vegetables and field crops during the transition from conventional to organic production.We recorded the time to hand-weed and computed the labor cost of using CP and NST strategies. Yield and quality of tomato and cabbage were determined each year to study the impact of weed management systems on these parameters. We hypothesized that yields in NST plots would be no higher than yields in

CP plots. Harvest ease was not measured directly, but observations were taken.

MATERIALS AND METHODS

Field studies were conducted at the Ohio Agricultural Research and

Development Center (OARDC), Wooster, Ohio (latitude 400 47’ N and longitude 810

55’ W and of elevation 310 m) from 2001 to 2004. Materials and methods used in the research, including pest management, are fully described in chapter 2 (Amisi, 2005). The field experiment was a 4-year rotation of processing tomatoes (Lycopersicon esculetum

L.) cv ‘Peto 696’1, fresh market cabbage (Brassica oleraceae L.) cv ‘Bravo’2, winter wheat (Triticum aestivum L.) cv ‘Carl’, and red clover (Trifolium pretense L.). Because experiments were initiated in the spring, spring wheat was used in 2001 instead of winter wheat. Tomato and cabbage seed were locally obtained and were neither certified organic nor treated. The study was established in soil that was previously in a 3-year rotation of corn, soybean, and forage. In April 2001, prior to spring-tillage and initiation of the transition, the entire area was sprayed with glyphosate (N-phosphono-methyl glycine) at rate of 1.0 kg ha-1 acid equivalent to kill perennial weeds.

The experimental design was a split plot in a randomized complete block with 4 replications. The rotational sequence and main- and sub-plot treatments were assigned to the field randomly. Weed management and soil amendment plots were designated for each crop in 2001 and were maintained throughout. The main plot treatments each year in cabbage and tomato were soil fertility amendments: no amendment (control), or composted dairy manure, or raw dairy manure (Tables 2.1 and 2.2). Soil amendments were applied in 9.1 m wide strips. Amendments were free of weed seeds (Amisi, 2005).

Each crop in the rotation had a total of 6 main plots 222 m2 [24.4 m wide x 54.9 m long]

(2 replications of each amendment). Soil amendments were not applied prior to planting clover or winter wheat. Sub-plot treatments were the weed control strategies. Every crop in the rotation had a total of 24 sub-plots, each 56 m2 [6.1 m wide x 9.1 m long]. Fields were mold-board plowed and disc harrowed in April each year prior to planting. Each crop in the rotation had an area of 1338 m2 [55 m x 24.3 m].

Tomato and cabbage seedlings were transplanted into the respective plots during

June each year except 2004. Winter wheat and red clover were seeded at 112.2 kg/ha and

22.4 kg/ha respectively. Weed management corresponded with standard practices used by local organic farmers. In other words, weed control efforts (CP and NST treatments) were systematic and intensive in tomatoes and cabbage. Weed control treatments were applied in wheat and clover only on the rare occasions when summer annual weeds occurred in abundance. Otherwise, clover was harvested (both CP and NST plots) twice each year, effectively removing the few weeds that occurred before seed were produced.

Tomato and cabbage plots designated to receive the CP treatment were maintained weed-free by hand-weeding and hoeing for 5 weeks. The critical weed-free period for cabbage is 3 to 4 weeks (Horng, 1980; Miller and Hoppen, 1991; Zimdahl, 2004) after planting, while for tomato it is 4 to 5 weeks after transplanting (Weaver and Tan, 1983;

Weaver, 1984; Zimdhal, 2004). Plots designated as NST were kept totally weed-free for the entire growing season. Hand weeding was accomplished with a Dutch hoe. A cultivator was also used to kill weeds between rows of cabbage in 2002 and 2003. NST plots in wheat stubble were sprayed with “Burn Out” (20% acetic acid)3 on September 6,

2002 to control summer annual weeds that had emerged. NST plots in clover were

mowed on September 11, 2001, June 24 and August 28, 2002, June 25 and August 11,

2003, and June 24 and August 8, 2004 to control summer annual weeds. In these instances when weeds were controlled in NST wheat and clover plots, weed control was not applied in the respective CP plots.

During the growing season, management practices like irrigation, disease and insect control complied with standards required for organic certification and were carried out as needed for both the tomato and cabbage. Weed seedlings in cabbage and tomato were identified and counted in 3 (0.5 x 0.5 m) quadrants/sub-plot 2, 3, and 5 weeks after transplanting each crop. After counts were taken, each plot was weeded by hand. Hand weeding was carried out in all NST plots for the entire growing season of the tomato and cabbage crops. In 2001 and 2002, the time to weed each sub-plot (area 56 m2) was recorded to the nearest minute. In 2003, the time required to weed only an area of 9.29 m2 within each subplot was recorded. This area consisted of two treatment rows of tomato or cabbage.

Tomato fruit were harvested on September 9, 2001, September 12, 2002 and

September 22, 2003. Cabbages were harvested on September 25, 2001, and on

September 16 in 2002 and 2003. Yield for both crops was recorded.

Data on time taken to hand-weed were subjected to ANOVA at P ≤ 0.05 using

PROC GLM (SAS version 8, 1999). All data met the assumptions of ANOVA, and did not require transformation. Interactions were not detected between weed treatments (CP and NST) and amendments (control, compost or manure). Data reported are restricted to those of the sequence 2001 Clover, 2002 Tomato, 2003 Cabbage (rotation 1), the only

rotation that reflects three consecutive years in which the NST was implemented. The average time (in hours/ha) to weed CP plots for 5 weeks and to weed NST plots was calculated for the years 2002 and 2003. Statistically, significant differences were not detected between the two weed management strategies for time taken to hand weed.

Yield data were analyzed at P ≤ 0.05 using PROC GLM (SAS version 8, 1999).

Tomato and cabbage were graded into marketable and non-marketable. Data analysis was done by ANOVA, with both weed management and amendments as main and interactive effects.

RESULTS AND DISCUSSION

Time taken to hand-weed and labor cost

Summer annual weeds, mainly redroot pigweed and common lambsquarters, were removed from red clover NST plots on September 11, 2001 by mowing all vegetation 10 cm above the ground. Rainfall during June and July 2002 was 18 % to

79% respectively below the 30 year average (Appendix Table D.1) and weed pressure was low, especially from 5 weeks after transplanting (WAT) forward (Amisi, 2005,

Table 2.4 and 2.5). During the first 5 WAT in 2002, 42% fewer pigweed and lambsquarter seedlings were observed in NST than in CP plots (Amisi, 2005, Table 2.4).

However, the time required to weed NST and CP plots, 21.3 and 23 h, respectively, was similar (Table 3.1). Subsequently, 21.1 additional h (92% more) were required to weed the NST plots until tomato harvest (Table 3.1). Nine more weeks of weeding occurred after the 5 week CP in NST plots. Additional hours were spent walking and hand pulling

occasional individuals. In some instances, very minimal hand hoeing was required to remove weeds. Weed pressure after the 5 week CP was less than weed pressure during the CP.

Tomatoes were followed by cabbage in 2003. Rainfall was greater or equal to the

30 year average in 2003 (Appendix Table D.1), and weed pressure was correspondingly higher and more uniform throughout the season (Amisi, 2005, Tables 2.4 and 2.7). Fifty four % fewer lambsquarter and pigweed seedlings were observed in NST than in CP plots during the first 5 WAT. Less time (8.1 h) was required to weed NST plots during the CP; however, this was not significant. Labor needed to keep the NST plots weed-free for the remainder of the growing season was only 33% more than that required for the

CP plots, even though weed pressure was greater, overall, in 2003 than in 2002 (Table

3.1).

The cost of labor (based on $6/hr) for weed control in both years was significant, regardless of strategy, ranging from an average of $192/ha with the CP strategy to

$296/ha with the NST. However, these costs need to be placed in perspective. Plastic mulch used to control weeds in vegetables, exclusive of application and environmental costs, will easily range from $500 to 700/ha (Burns, 1998).

Our results indicate that it is expensive to use the NST as a weed management strategy. Norris indicated it might be cost prohibitive in low-value crops (Norris, 2000).

However, our research indicates that for farms with weed pressure similar to what we experienced, costs during the initial years would be acceptable. In the long term, labor costs would decrease as weed numbers decreased.

Yield and quality

Weed management strategies did not affect yield of tomato or cabbage.

Controlling weeds during the 5 week CP optimized crop yield; no additional yield occurred when weeds were controlled until harvest. Thus, the CP might be a means to increase profit during the transition period; however, in future years weed control costs might escalate due to expanding soil weed seedbanks. Compost and manure amendments had yield impacts for both crops. However, the effect of amendments was not significant for tomato yield parameters in 2001 and 2003 (Tables 3.2 and 3.4). In 2001 bacterial canker (Clavibacter michiganensis) was observed in the tomato plots and this could have affected the yield. In contrast, cabbage yield parameters were sensitive to soil amendments each year. Differences in timing of peak demand for nutrients between tomato and cabbage, relative to their release from organic matter, may have contributed to this contrast. In 2001, no effect of amendment was observed in tomato yield, probably because the residual nutrients available were adequate to meet the crops needs.

Apparently, residual fertility from the conventionally grown corn, soybean, and forage rotation provided sufficient nutrients for tomatoes in 2001. Mineralization of nitrogen from the preceding clover green manure crop evidently was sufficient to meet demands for nutrients in tomato in 2002 and 2003. However, it should be noted that total fruit/ha was higher in manure and compost amended soils in 2002 (Table 3.3). The significant impact of manure and compost on all parameters of cabbage yield suggests that timing

of release of nutrients and/or the quantity from residuals may have been inadequate for the crop (Tables 3.5 to 3.7).

CONCLUSION

In general, the NST weed management strategy took longer and was more expensive to achieve compared to CP. This is expected in the initial years of NST adoption. In the long-term, as the weed population decreases, less time will be taken to achieve NST. In addition, the future labor costs incurred will be reduced. Weed management strategies did not affect yield of tomato or cabbage. However, the long term use of CP may lead to a larger weed seedbank and thus increase weed control costs.

Cabbage yield was more sensitive to amendments than tomato and this could be due to the differences in the demand for nutrients between the 2 crops.

SOURCE OF MATERIALS

1. Seminis Vegetables Seeds, Oxnard California

2. Harris Seeds, Rochester, New York

3. St. Gabriels Laboratories, Gainesville, Virginia

Time (hours/ha) Cost (US $/ha) Rotation sequence CP NST NST CP NST NST 5 wk 5 wk total 5 wk 5 wk total Rotation 1 Clover 2001 - - - - Tomato 2002 23.0 21.3 44.1 138.0 128.0 264.7 Cabbage 2003 41.0 32.9 54.5 246.2 197.3 327.0 Wheat 2004 - - - - Rotation 2 Tomato 2001 - - - - Cabbage 2002 11.9 11.6 28.7 71.3 69.9 172.5 Wheat 2003 - - - - Clover 2004 - - - - Rotation 4 Wheat 2001 - - - - Clover 2002 - - - - Tomato 2003 32.1 32.6 51.9 192.8 195.9 311.4 Cabbage 2004 - - - -

Table 3.1: Effect of weed management strategies (CP and NST) on average time taken (hours/ha) and cost of labor (US $/ha) to hand-weed. Abbreviations: dash ( - ) = no data (no vegetable crop was grown in 2004); CP = critical period for 5 weeks after planting and NST = no seed threshold for the first 5 weeks and the entire season.

Marketable Marketable Total fruit yield Total yield fruit (per Treatment (Mg⋅ha-1) (Mg⋅ha-1) (per hectare) hectare) Amendment Control 48.27 87.63 1,139,788 2,859,150 Manure 50.29 87.00 1,046,121 2,157,387 Compost 57.34 100.28 1,179,676 2,583,984 Weed treatment CP 57.71 93.63 1,233,539 2,750,938 NST 48.23 89.64 1,025,802 2,365,536

Table 3.2: Effect of soil amendments (no amendment (control), raw manure or composted manure) and weed treatments on yield of organic processing tomatoes in 2001.

Marketable Marketable Total fruit yield Total yield fruit (per Treatment (Mg⋅ha-1) (Mg⋅ha-1) (per hectare) hectare) Amendment Control 76.21 94.31 1,789,539 2,426,496b Manure 82.56 103.21 2,125,855 2,951,147a Compost 78.96 98.24 2,019,540 2,802,265a Weed treatment CP 76.56 96.28 1,910,304 2,649,662 NST 81.93 100.9 2,046,319 2,803,610

Marketable Marketable Total fruit yield Total yield fruit (per Treatment (Mg⋅ha-1) (Mg⋅ha-1) (per hectare) hectare) Amendment Control 63.42 113.63 1,031,403 1,832,446 Manure 82.56 119.70 976,637 1,901,978 Compost 74.53 133.94 1,116,306 2,219,378 Weed treatment CP 65.56 120.59 1,035,777 1,950,126 NST 81.46 124.24 1,047,120 2,019,076

Table 3.4: Effect of soil amendments (no amendment (control), raw manure, or composted manure) and weed treatments on yield of organic processing tomatoes in 2003.

Treatment Marketable yield (Mg⋅ha-1) Total yield (Mg⋅ha-1) Amendment Control 37.49 71.52b Manure 64.61 85.08ab Compost 65.35 115.66a Weed treatment CP 50.73 87.49 NST 60.90 94.01

Treatment Marketable yield (Mg⋅ha-1) Total yield (Mg⋅ha-1) Amendment Control 10.76 65.64b Manure 13.65 77.82a Compost 15.52 85.50a Weed treatment CP 13.35 78.21 NST 13.27 74.43

Treatment Marketable yield (Mg⋅ha-1) Total yield (Mg⋅ha-1) Amendment Control 54.92b* 83.44b** Manure 91.29a 123.51a Compost 83.22a 139.23a Weed treatment CP 78.33 111.48 NST 74.62 119.31

Table 3.7. Effect of soil amendments (no amendment (control), raw manure, or composted manure) and weed treatments on yield of organic cabbage in 2003. Means followed by different letters under amendment columns within each row are significantly different at P ≤ 0.05 (*) and P ≤ 0.01 (**).

LIST OF REFERENCES

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Amisi, K. J. 2005. Strategies for managing weeds in a wheat, red clover, vegetable crop rotation transitioning to organic production Ph D. Dissertation. The Ohio State University. 2004.

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Cousens, R. 1987. Theory and reality of weed control thresholds. Plant Protection Quarterly 2: 13-20.

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Horng, Liang-Chi. 1980. Interference of pale smartweed (Polygonum lapithifolium) with cabbage (Brassica oleracea). Weed Sci. 28: 381-384.

Jones, R. E. and R. W. Medd. 2000. Economic thresholds and the case for longer term approaches to population management of weeds. Weed technol. 14: 337-350.

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Knezevic, S. Z., S. P. Evans, E. E. Blankenship, R. C. Van Acker and J. L. Lindquist. 2002. Critical period for weed control: the concept and data analysis. Weed Sci. 50: 773-786.

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CHAPTER 4

REDROOT PIGWEED (AMARANTHUS RETROFLEXUS L.) GROWTH IN

COMPOST- AND MANURE-AMENDED SOIL MIXES

Karen Amisi and Doug Doohan

ABSTRACT

The objective of this study was to compare the growth of redroot pigweed in compost- and manure-amended soil mixes. Greenhouse experiments were conducted to observe growth of redroot pigweed seedlings in three soil/composted dairy manure mixes, three soil/raw dairy manure mixes, and soil alone. Greenhouse environmental conditions were at 23 - 27 °C for 16 hrs and 18 - 21 °C for 8 h. with a relative humidity of 90.5%. Irradiance was natural light, supplemented by sodium lamps that provided 350

µ mol m-2 s-1 photosynthetic photon flux density (PPFD) for 16 h. The experimental unit was a 3.8 L pot containing 6 redroot pigweed plants. Data recorded were: 1) plant height, 2) internode length, 3) number of leaves and leaf area, 4) shoot- and root-fresh weights, and 5) seed number. For every parameter measured, soil:manure mixes retarded plant development compared to soil alone (the control) or soil:compost mixes. For most

parameters, even the lowest ratio of soil:manure reduced growth relative to soil. Redroot pigweed growth responded inversely to increasing proportions of manure in the media.

Plant growth response to compost in the media was somewhat variable from parameter to parameter, but was always equal to or greater than growth in soil. Redroot pigweed growth was greatest in compost/soil mixes > soil > manure/soil mixes. Internode length was greatest in compost-amended soils (3.2-4.5 cm), and shortest in manure-amended soils (0.2-0.7 cm). At 63 DAP, redroot pigweed plants growing in compost/soil treatments were the tallest (58.8-70.5 cm), whereas those growing in the highest ratio of manure:soil were the shortest (21.6-48.3 cm). At 30 DAP, leaf area and number were highest for plants growing in soil with the highest rate of compost (42.5-140.3 cm2 and

22-42, respectively), and lowest for plants growing in soil with the highest rate of manure (3.1-12.4 cm2 and 8-12, respectively). In addition, plant fresh and dry weights were highest in compost treatments (33.5-53.6g and 6.8-10.9g, respectively), and lowest in the highest manure treatment (5.6-20.6g and 0.5-3.6g, respectively). The number of seeds/plant were also highest in compost-amended soils (399-1416) and lowest in manure-amended soils (23-275).

INTRODUCTION

Soil is a fundamental resource in agro-ecosystems (Mitchell et al., 2000).

Agricultural practices that impact the soil affect the myriad of micro- and macro- organisms that inhabit the soil matrix. Practices that most visibly impact weeds include tillage, crop rotation, and the input of synthetic and organic fertilizers (Gallandt et al.,

1999). Fertilizer is added to improve crop yield, but many weeds are more competitive with crops at higher nutrient levels. At high weed densities, added fertilizer, particularly nitrogen (N), favors weed over crop growth (Zimdahl, 2004). Nitrogen, the most limiting nutrient, is known to influence plant community structure (Tilman, 1985, 1986;

DiTomaso, 1995). Early and late succession species differ in their ability to compete for soil N (Tilman, 1986).

Addition of organic materials, like animal manure and compost, has long been recognized to markedly improve soil quality (Magdoff, 1992). Organic materials promote crop growth and yield by improving soil fertility, water availability, and aeration (Doran, 1995; Drinkwater et al., 1995), and can be used in various combinations with several cover crops to provide diversified soil amendment systems adapted to local conditions (Gallandt et al., 1999). Amending soils with organic material may also improve crop performance by reducing pest pressure (Drinkwater et al., 1995; Partriquin et al., 1995; van Bruggen, 1995; Liebman and Ohno, 1998). Organic matter amendments have been shown to render crops less attractive to insect pests (Phelan et al., 1995), and reduce crop disease problems by promoting better soil structure, more vigorous root systems, and greater populations of soil microorganisms that antagonize, outcompete, parasitize, or consume crop pathogens (van Bruggen, 1995).

Soil improving practices affect the soil environment through their influence on bulk density, water relations, and soil chemistry. These changes may influence the abundance and filling of safe sites by germinating seeds. The relative ability of crops and weeds to capture safe sites leads to the phenomena of interference between weeds and

crops and ultimately to crop yield loss, weed biomass, and seed production. Soil improving practices may contribute to differential species performance through temporal or spatial resource supply (Gallandt et al., 1999).

Weed growth and interspecific interference may also be affected by changes in soil microorganisms brought about through addition of organic materials. Deleterious bacteria have been shown to selectively inhibit weed seedling growth without harming crop plants (Gallandt et al., 1999). Soils can be managed to encourage the activity of deleterious rhizobacteria (Boyetchko, 1996). Hence the goals in the use of soil management to manipulate weed dynamics is to reduce the persistence of seeds in the soil, the abundance and/or filling of safe sites, and the crop yield loss per individual weed (Gallandt et al., 1999).

Livestock manure and compost are key fertilizers in organic and sustainable soil management. Manure is applied to the field in either a raw or composted state. Raw manures presents a number of potential problems including the presence of chemical and microbial contaminants (Anon, 1997), a tendency to impart off-flavors and odors to vegetables due to release of phenolic compounds during breakdown in the soil (Kinsey,

1994), creation of imbalances in soil fertility especially high phosphate and potash levels, the tendency to acidify soils with continual use, increased weed problems due to the presence of weed seed (Eghball and Lesoing, 2000), and pollution that can affect human health (CAST, 1999).

In contrast, compost is a homogenous and friable mixture primarily composed of stabilized organic matter derived by biological decomposition of natural organic material

by soil organisms (Composting Fact Sheet, 1996). Composting can significantly reduce the environmental problems associated with use of manure (Carr et al., 1995; Wang et al., 2004). Compost is low in soluble salts and less likely to cause nutrient imbalances in vegetable crops (Kuepper, 2003). Composts have been used extensively in intensive vegetable production to improve soil quality and sustain productivity (Maynard, 1994).

Compost improves biological, chemical and physical properties of amended soils, and can provide effective biological control of disease caused by soilborne plant pathogens

(Kwok et al., 1987; Hoitink et al., 1991; Abbasi et al., 2002). Composts also reduce the severity of diseases caused by foliar pathogens (Miller et al., 1997).

Studies have been conducted to determine the impact of organic soil amendments on crops, but very little is known about the impact of soil amendments on weeds or crop- weed interactions under organic production. Because weed management is one of the most important production problems experienced by organic farmers (Walz, 1999), it is critically important to determine the likely impact of organic amendments on weeds. Can organic amendments be used to influence weed community structure, periodicity of germination, growth and reproduction? The objective of this study was to compare the growth of redroot pigweed in compost- and manure-amended soil mixes.

MATERIALS AND METHODS

We chose redroot pigweed (Amaranthus retroflexus) as a model weed for this study. Pigweeds (Amaranthus spp.) are common throughout the United States (Bridges,

1992; Holm et al., 1997). Aggressive growth habit and prolific seed production allow

pigweeds to compete favorably with crops for water, light, and nutrients (Barkely, 1986;

Murphy et al., 1996; Knezevic et al., 1997). Redroot pigweed is one of the most frequent problem weeds in organic fields (Walz, 1999).

Trials (Trial 1 and 2) were carried out in 2004 in the greenhouse to observe growth of redroot pigweed seedlings in soils amended with raw and composted dairy cow manure. Three rates, each, of manure and compost were used, for a total of 7 growing media (3 soil/compost mixes, 3 soil/manure mixes, and soil only). Soil used in these experiments was collected from the organic vegetable transition plots on the campus of the Ohio Agricultural Research and Development Center (OARDC) (Amisi,

2005). Characteristics of 2004 compost and manure are detailed in Tables 2.1 and 2.2.

Growing media were mixed to deliver 101 kg/ha of N, based upon 50% immediate availability. No additional nutrients were applied throughout the study.

The experimental design was completely random with 4 replicates and 7 treatments. Each trial had 28 pots, each with a volume of 3.78 L (17.78 cm in diameter).

Pots were filled with experimental media (Table 4.1) and randomly arranged on a greenhouse bench. One hundred redroot pigweed seeds were sown in each pot. Pots were periodically rearranged on the bench, so as to give each pot a chance to experience the different micro-environments in the room. Each pot received 128 ml of water daily by drip irrigation. The greenhouse environmental conditions were maintained at 23.3 - 26.6

°C for 16 hrs and 18.3 - 21.1 °C for 8 h, with a relative humidity of 90.5%. Irradiance was natural light supplemented by Sodium lamps that provided 350 µ mol m-2 s-1 photosynthetic photon flux density (PPFD) for 16 h.

The growth experiment was carried out for 63 days (9 weeks) and was repeated.

Two weeks after emergence, seedlings were pulled out to leave only 6 plants/pot.

Throughout the study period, data were recorded on the following parameters: 1) plant height (cm) 14-63 days after planting (DAP), 2) internode length (cm) 14 DAP, 3) number of leaves and leaf area 18, 23, and 30 DAP (leaf area was measured using a belt fed leaf area meter1), and 4) shoot- and root-fresh weights 63 DAP. For these data, one plant from each pot was tagged and left to grow for the entire study. At harvest, the plants were cut at soil level and shoot fresh weight taken. Roots were carefully removed from the pots, rinsed with cold water to remove media and root fresh weight was recorded. Plant shoots and roots were dried at 112 °C for 72 h and weighed. Seeds were collected from the dry plant shoots and counted.

Statistical analyses were performed using SAS statistical software version 8.0

(SAS, 1999). Analysis of variance was performed using the general linear model (PROC

GLM) procedure of SAS and means separated by Fishers’ Protected LSD at the 5 % level.

RESULTS AND DISCUSSION

Soil amendments affected redroot pigweed internode length and plant height, number of leaves and leaf area, fresh and dry weights and seed production. For every parameter measured, soil:manure mixes retarded plant development compared to soil alone (the control) or soil:compost mixes. For most parameters, even the highest ratio of soil:manure (SM1) reduced growth relative to soil (control). Redroot pigweed growth

was inversely proportional to increasing concentrations of manure in the media. Growth response to compost in the media was somewhat variable from parameter to parameter, but was always equal to or greater than growth in soil (control).

Manure and compost significantly affected internode length (Table 4.2). At 14

DAP, internode length was greater in compost-amended soils than in the control soil, except with SM1in Trial 1. In contrast, internode length was reduced when manure was mixed with soil. In the first trial, this was observed at soil:manure ratios of SM2 and

SM3, whereas the effect was not significant in every soil:manure mix in Trial 2 (Table

4.2). Internode length in Trial 1 was greater in soil/compost mixes than in soil/manure mixes, with SC1 having the greatest length (4.5 cm) and SM1 the least (0.7 cm). In Trial

2, similar results were observed; however, internodes were longest with SC3 (3.2 cm) and shortest with SM3 (0.2 cm).

Treatment effects were significantly different from each other (P ≤ 0.05) for plant height over the experiment period of 9 weeks for both trials (Tables 4.3 and 4.4).

Pigweed plants growing in compost-amended soils were taller than those growing in manure-amended soils. At 63 DAP, redroot pigweed growing in treatments SC1 (70.5 cm) and SC3 (58.8 cm) were the tallest in Trial 1 and 2, respectively, whereas plants were shortest in treatment SM3 (48.3 and 21.6 cm for Trial 1 and 2, respectively).

Plant leaf area and number differed significantly (P ≤ 0.05) between compost- and manure-amended soils in both trials (Tables 4.5 and 4.6). Plants growing in compost-amended soils had larger leaf areas than those in manure-amended soils. Thirty

DAP, leaf area was greatest for SC3 (140.3 and 42.5 cm2) and lowest for SM3 (12.4 and

3.1 cm2) in Trials 1 and 2, respectively. Results for plant leaf number showed similar trends. At 30 DAP, leaf number was highest in SC3 (42 and 22) and lowest in SM3 (12 and 8) in Trials 1 and 2, respectively.

Treatments differed significantly (P ≤ 0.05) from each other for both fresh and dry weights, and number of seeds/plant at harvest in both trials (Table 4.7). Plants growing in compost-amended soils had higher fresh and dry weights than those growing in manure-amended soils. Plant fresh weights were highest in treatments SC2 (53.6 g) and SC3 (33.5 g) for Trials 1 and 2, respectively, and lowest in SM3 (20.6 and 5.6 g for

Trials 1 and 2, respectively). Plant dry weights were highest in treatments SC2 (10.9 g) and SC3 (6.8 g) for Trials 1 and 2, respectively, and lowest in treatment SM3 (3.6 and

0.5 g for Trials 1 and 2, respectively). Plants in Trial 2 had less biomass overall than those in Trial 1, as reflected in their fresh and dry weight values.

The number of seeds/plant was higher for plants grown in compost-amended soils than in manure-amended soils. Treatments SC2 (1416) and SC3 (399) had the highest number of seeds/plant in Trial 1 and 2, respectively. The treatment SM3 had the lowest number of seeds/plant (275 and 23 in Trials 1 and 2, respectively), although it was not significantly different from seed production in soil alone (Table 4.7).

Fewer flowering stalks were observed on plants growing in manure- than in compost-amended soil (observations only). In addition, treatments affected seed ripeness

(expressed as seed color). Redroot pigweed plants growing in manure-amended soils produced seeds with a lighter color, whereas those growing in compost-amended soils had a darker color (black) indicating maturity (observations only).

This experiment was conducted twice previous to the experiments reported in this chapter. Each time similar results were obtained. In the previous series of the experiments, at least 2 different batches of compost and manure (2002 and 2003) were used with similar results.

In these experiments, manure had a profound negative effect on pigweed growth with respect to the parameters measured. Manure delayed growth of pigweed, especially when large quantities were incorporated in the soil (SM3 > SM2 > SM1). In addition, manure decreased the number of pigweed seeds/plant.

In these experiments, raw dairy cow manure negatively impacted growth and seed production of redroot pigweed, relative to non-amended soil. In contrast, composted dairy manure increased pigweed growth and seed production. Both trends were generally rate-dependent; ie as the ratio of amendment to soil increased, growth decreased proportionately in manure-amended soils and increased proportionately in compost-amended soils (Appendix Tables E.1 - E.6).

Collectively, the data suggest that amending soils with raw dairy manure would reduce the competitiveness of redroot pigweed; whereas, amending with composted manure would increase competitiveness. However, inferences from these results must be treated very conservatively, because manure and compost are biological products of potentially great variability. Source, storage and handling of manure and compost may greatly affect their impact on the soil environment and performance of plants growing in the soil. Much more research is required to determine if these trends extrapolate across weed species, manures from different livestock, and composts from different raw

materials or composting processes. Research is also needed to investigate mechanisms involved and the role of individual constituents of manure and compost in the phenomena we observed. Finally, research is required to determine the relative impact of manure and compost on the competitive ability of redroot pigweed with crops. Is crop growth diminished when raw dairy manure is used as an amendment and how do crops compare relatively with the performance of redroot pigweed?

CONCLUSIONS

These results imply that amending soil with livestock manure may affect weed management in both the short- and long-term. For short-term management, manure- amended soils may reduce pigweed seedling emergence and growth, while for long-term management, manure may reduce pigweed seed production and thus help reduce the resident seedbank.

There is a need for more research on how soil amendments affect weed seed survival, seedling recruitment, and growth. Amendment related factors that might affect weed dynamics include changes in communities of microbes and insects that attack weed seeds and seedlings, alterations of soil physical properties influencing safe sites for weed germination and establishment, increased concentrations of amendment-derived phytotoxins and growth stimulants, shifts in the timing of nutrient availability, and differential responses between crop and weed species to these factors (Gallandt et al.,

1999; Liebman and Davis, 2000).

SOURCES OF MATERIALS

1. (LI- COR LI-3100 LI-COR Inc P.O. Box 4425 Lincoln, NE 68504).

Treatment Soil: Amendment (g) Comments SC1 Soil /Compost 1 4535 : 290.4 Compost field plots SC2 Soil/Compost 2 4535 : 588.8 SC3 Soil/Compost 3 4535 : 871.2 SM1 Soil/Manure1 4535 : 666.8 Manure field plots SM2 Soil/Manure 2 4535 : 1333.6 SM3 Soil/Manure 3 4535 : 2000.4 Soil only 4535 : 0 Control field plots

Table 4.1: Media mixes used in redroot pigweed growth studies.

Treatment Soil : Amendment (g) Trial 1 Trial 2 SC1 4535 : 290.4 4.5 a 2.7 a SC2 4535 : 588.8 3.3 b 2.5 ab SC3 4535 : 871.2 3.5 b 3.2 a SM1 4535 : 666.8 2.0 c 0.7 c SM2 4535 : 1333.6 1.0 d 0.8 c SM3 4535 : 2000.4 0.7 d 0.2 c SOIL ONLY 4535 : 0 1.9 c 1.8 b LSD 0.73 0.74

Days after Planting Treatment Soil : Amendment (g) 18 23 30 35 42 49 56 63 SC1 4535 : 290.4 8.3 a 11.0 a 16.7 a 22.5 a 35.1 a 49.9 a 64.8 a 70.5 a SC2 4535 : 588.8 7.0 ab 10.8 a 17.4 a 22.3 a 34.4 a 49.2 a 63.9 a 70.2 a SC3 4535 : 871.2 7.0 ab 9.6 a 15.3 ab 20.3 ab 32.1 a 46.5 a 60.8 ab 67.0 ab SM1 4535 : 666.8 5.5 c 7.6 b 13.1 bc 18.5 b 31.0 a 44.9 a 56.5 bc 61.2 bc SM2 4535 : 1333.6 3.9 d 5.3 c 9.0 d 12.1 cd 20.7 b 32.5 bc 44.6 de 50.6 d SM3 4535 : 2000.4 2.6 e 3.7 c 6.8 d 9.1 d 15.6 c 26.6 c 41.0 e 48.3 d SOIL ONLY 4535 : 0 5.4 c 7.7 b 12.0 c 14.8 c 22.6 b 35.7 b 50.6 cd 58.6 c LSD 1.27 1.68 2.49 3.39 5.08 6.69 7.15 7.11 96

Table 4.3: Effect of compost- and manure-amended soils on plant height (cm) of redroot pigweed in Trial 1. Means followed by different letters within a column are different at P ≤ 0.05.

Days after Planting Treatment Soil : Amendment (g) 18 23 30 35 42 49 56 63 SC1 4535 : 290.4 5.7 a 7.1 b 11.2 b 15.1 ab 24.7 ab 37.0 ab 49.7 ab 55.1 a SC2 4535 : 588.8 6.2 a 7.8 ab 11.9 ab 15.2 ab 23.4 ab 34.4 b 44.7 ab 49.1 ab SC3 4535 : 871.2 6.6 a 8.4 a 13.4 a 17.7 a 28.6 a 42.0 a 54.1 a 58.8 a SM1 4535 : 666.8 3.7 a 4.8 c 7.7 c 9.9 c 15.6 cd 24.3 cd 33.7 c 40.4 b SM2 4535 : 1333.6 3.2 a 4.1 c 6.5 cd 8.4 cd 13.4 de 22.0 d 32.8 c 39.5 b SM3 4535 : 2000.4 3.0 a 3.7 c 5.4 d 6.6 d 9.0 e 12.2 e 17.8 d 21.6 c SOIL ONLY 4535 : 0 5.9 a 7.2 ab 10.6 a 13.1 b 20.60 bc 31.6 c 43.8 b 50.1 ab LSD 1.16 1.32 2.07 3.09 5.44 7.47 9.5 10.80 97

Table 4.4: Effect of compost- and manure-amended soils on plant height (cm) of redroot pigweed in Trial 2. Means followed by different letters within a column are different at P ≤ 0.05.

Number of Leaves Leaf area Treatment Soil : Amendment (g) 18 23 30 18 23 30

SC1 4535 : 290.4 11.8 a 14.8 a 36.3 ab 26.6 a 38.4 a 81.7 b SC2 4535 : 588.8 8.8 b 14.5 ab 41.5 a 15.0 b 37.1 ab 135.0 a SC3 4535 : 871.2 8.5 b 14.8 a 42.0 a 16.8 b 44.3 a 140.3 a SM1 4535 : 666.8 8.0 bc 10.3 bc 34.8 ab 7.0 c 15.0 cd 63.7 bc SM2 4535 : 1333.6 7.0 bc 7.0 c 18.5 cd 2.7 cd 2.8 d 23.6 cd SM3 4535 : 2000.4 5.8 c 7.0 c 12.3 d 1.1 d 1.4 d 12.4 d SOIL ONLY 4535 : 0 7.3 bc 10.8 abc 27.3 bc 6.8 c 23.7 bc 70.4 bc 98 LSD 2.39 4.27 12.15 5.44 13.67 46.79

Number of Leaves Leaf area Treatment Soil : Amendment (g) 18 23 30 18 23 30 SC1 4535 : 290.4 7.0 a 8.3 a 21.3 a 5.0 ab 8.1 ab 33.2 ab SC2 4535 : 588.8 7.0 a 8.0 a 18.5 ab 6.2 a 6.4 bc 28.7 ab SC3 4535 : 871.2 6.3 ab 6.8 ab 22.0 a 7.0 a 6.4 bc 42.5 a SM1 4535 : 666.8 6.0 ab 6.3 ab 14.8 abc 1.6 bc 2.3 cd 16.6 bc SM2 4535 : 1333.6 5.8 ab 6.0 ab 11.0 bc 0.9 bc 1.8 d 9.8 c SM3 4535 : 2000.4 4.8 b 5.3 b 7.5 c 0.4 c 0.5 d 3.1 c SOIL ONLY 4535 : 0 6.0 ab 6.8 ab 23.0 a 6.2 a 11.4 a 40.3 a LSD 2.16 2.32 9.38 4.20 4.60 17.94 99

Table 4.6: Effect of compost- and manure-amended soils on number of leaves and leaf area (cm2) of redroot pigweed (18, 23, and 30 DAP) in Trial 2. Means followed by different letters within a column are different at P ≤ 0.05.

Trial 1 Trial 2 Soil : Fresh Number of Fresh Number of Treatment Amendment (g) weight Dry weight seeds weight Dry weight seeds SC1 4535 : 290.4 37.3 bc 7.6 b 739.8 ab 29.0 ab 5.5 ab 360.5 a SC2 4535 : 588.8 53.6 a 10.9 a 1415.8 a 21.4 bc 3.9 bc 318.0 a SC3 4535 : 871.2 43.7 b 8.4 b 1268.3 a 33.5 a 6.8 a 399.0 a SM1 4535 : 666.8 41.0 bc 8.2 b 937.0 ab 14.9 c 2.3 cd 230.5 ab SM2 4535 : 1333.6 27.1 de 4.6 cd 412.0 b 14.5 c 2.3 cd 186.0 ab SM3 4535 : 2000.4 20.6 e 3.6 d 275.5 b 5.6 d 0.5 d 22.8 b SOIL ONLY 4535 : 0 34.0 cd 6.3 bc 578.0 b 20.0 c 3.3 c 257.8 ab 100 LSD 8.65 2.16 679.76 8.60 1.86 238.72

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